drivers/net/tap.c | 115 +++++++++++++++++++++++++++++++-- drivers/net/tun.c | 136 +++++++++++++++++++++++++++++++++++---- drivers/vhost/net.c | 90 +++++++++++++++++--------- include/linux/if_tap.h | 15 +++++ include/linux/if_tun.h | 18 ++++++ include/linux/ptr_ring.h | 54 +++++++++++++--- 6 files changed, 367 insertions(+), 61 deletions(-)
This patch series deals with TUN, TAP and vhost_net which drop incoming
SKBs whenever their internal ptr_ring buffer is full. Instead, with this
patch series, the associated netdev queue is stopped before this happens.
This allows the connected qdisc to function correctly as reported by [1]
and improves application-layer performance, see our paper [2]. Meanwhile
the theoretical performance differs only slightly:
+------------------------+----------+----------+
| pktgen benchmarks | Stock | Patched |
| i5 6300HQ, 20M packets | | |
+------------------------+----------+----------+
| TAP | 2.10Mpps | 1.99Mpps |
+------------------------+----------+----------+
| TAP+vhost_net | 6.05Mpps | 6.14Mpps |
+------------------------+----------+----------+
| Note: Patched had no TX drops at all, |
| while stock suffered numerous drops. |
+----------------------------------------------+
This patch series includes TUN, TAP, and vhost_net because they share
logic. Adjusting only one of them would break the others. Therefore, the
patch series is structured as follows:
1+2: New ptr_ring helpers for 3 & 4
3: TUN & TAP: Stop netdev queue upon reaching a full ptr_ring
4: TUN & TAP: Wake netdev queue after consuming an entry
5+6+7: TUN & TAP: ptr_ring wrappers and other helpers to be called by
vhost_net
8: vhost_net: Call the wrappers & helpers
Possible future work:
- Introduction of Byte Queue Limits as suggested by Stephen Hemminger
- Adaption of the netdev queue flow control for ipvtap & macvtap
[1] Link:
https://unix.stackexchange.com/questions/762935/traffic-shaping-ineffective-on-tun-device
[2] Link:
https://cni.etit.tu-dortmund.de/storages/cni-etit/r/Research/Publications/2025/Gebauer_2025_VTCFall/Gebauer_VTCFall2025_AuthorsVersion.pdf
Links to previous versions:
V4:
https://lore.kernel.org/netdev/20250902080957.47265-1-simon.schippers@tu-dortmund.de/T/#u
V3:
https://lore.kernel.org/netdev/20250825211832.84901-1-simon.schippers@tu-dortmund.de/T/#u
V2:
https://lore.kernel.org/netdev/20250811220430.14063-1-simon.schippers@tu-dortmund.de/T/#u
V1:
https://lore.kernel.org/netdev/20250808153721.261334-1-simon.schippers@tu-dortmund.de/T/#u
Changelog:
V4 -> V5:
- Stop the netdev queue prior to producing the final fitting ptr_ring entry
-> Ensures the consumer has the latest netdev queue state, making it safe
to wake the queue
-> Resolves an issue in vhost_net where the netdev queue could remain
stopped despite being empty
-> For TUN/TAP, the netdev queue no longer needs to be woken in the
blocking loop
-> Introduces new helpers __ptr_ring_full_next and
__ptr_ring_will_invalidate for this purpose
- vhost_net now uses wrappers of TUN/TAP for ptr_ring consumption rather
than maintaining its own rx_ring pointer
V3 -> V4:
- Target net-next instead of net
- Changed to patch series instead of single patch
- Changed to new title from old title
"TUN/TAP: Improving throughput and latency by avoiding SKB drops"
- Wake netdev queue with new helpers wake_netdev_queue when there is any
spare capacity in the ptr_ring instead of waiting for it to be empty
- Use tun_file instead of tun_struct in tun_ring_recv as a more consistent
logic
- Use smp_wmb() and smp_rmb() barrier pair, which avoids any packet drops
that happened rarely before
- Use safer logic for vhost_net using RCU read locks to access TUN/TAP data
V2 -> V3: Added support for TAP and TAP+vhost_net.
V1 -> V2: Removed NETDEV_TX_BUSY return case in tun_net_xmit and removed
unnecessary netif_tx_wake_queue in tun_ring_recv.
Thanks,
Simon :)
Simon Schippers (8):
__ptr_ring_full_next: Returns if ring will be full after next
insertion
Move the decision of invalidation out of __ptr_ring_discard_one
TUN, TAP & vhost_net: Stop netdev queue before reaching a full
ptr_ring
TUN & TAP: Wake netdev queue after consuming an entry
TUN & TAP: Provide ptr_ring_consume_batched wrappers for vhost_net
TUN & TAP: Provide ptr_ring_unconsume wrappers for vhost_net
TUN & TAP: Methods to determine whether file is TUN/TAP for vhost_net
vhost_net: Replace rx_ring with calls of TUN/TAP wrappers
drivers/net/tap.c | 115 +++++++++++++++++++++++++++++++--
drivers/net/tun.c | 136 +++++++++++++++++++++++++++++++++++----
drivers/vhost/net.c | 90 +++++++++++++++++---------
include/linux/if_tap.h | 15 +++++
include/linux/if_tun.h | 18 ++++++
include/linux/ptr_ring.h | 54 +++++++++++++---
6 files changed, 367 insertions(+), 61 deletions(-)
--
2.43.0
On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: > This patch series deals with TUN, TAP and vhost_net which drop incoming > SKBs whenever their internal ptr_ring buffer is full. Instead, with this > patch series, the associated netdev queue is stopped before this happens. > This allows the connected qdisc to function correctly as reported by [1] > and improves application-layer performance, see our paper [2]. Meanwhile > the theoretical performance differs only slightly: About this whole approach. What if userspace is not consuming packets? Won't the watchdog warnings appear? Is it safe to allow userspace to block a tx queue indefinitely? -- MST
On Wed, Sep 24, 2025 at 3:18 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: > > This patch series deals with TUN, TAP and vhost_net which drop incoming > > SKBs whenever their internal ptr_ring buffer is full. Instead, with this > > patch series, the associated netdev queue is stopped before this happens. > > This allows the connected qdisc to function correctly as reported by [1] > > and improves application-layer performance, see our paper [2]. Meanwhile > > the theoretical performance differs only slightly: > > > About this whole approach. > What if userspace is not consuming packets? > Won't the watchdog warnings appear? > Is it safe to allow userspace to block a tx queue > indefinitely? I think it's safe as it's a userspace device, there's no way to guarantee the userspace can process the packet in time (so no watchdog for TUN). Thanks > > -- > MST >
On Wed, Sep 24, 2025 at 03:33:08PM +0800, Jason Wang wrote: > On Wed, Sep 24, 2025 at 3:18 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: > > > This patch series deals with TUN, TAP and vhost_net which drop incoming > > > SKBs whenever their internal ptr_ring buffer is full. Instead, with this > > > patch series, the associated netdev queue is stopped before this happens. > > > This allows the connected qdisc to function correctly as reported by [1] > > > and improves application-layer performance, see our paper [2]. Meanwhile > > > the theoretical performance differs only slightly: > > > > > > About this whole approach. > > What if userspace is not consuming packets? > > Won't the watchdog warnings appear? > > Is it safe to allow userspace to block a tx queue > > indefinitely? > > I think it's safe as it's a userspace device, there's no way to > guarantee the userspace can process the packet in time (so no watchdog > for TUN). > > Thanks Hmm. Anyway, I guess if we ever want to enable timeout for tun, we can worry about it then. Does not need to block this patchset. > > > > -- > > MST > >
On Wed, Sep 24, 2025 at 3:42 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > On Wed, Sep 24, 2025 at 03:33:08PM +0800, Jason Wang wrote: > > On Wed, Sep 24, 2025 at 3:18 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > > > On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: > > > > This patch series deals with TUN, TAP and vhost_net which drop incoming > > > > SKBs whenever their internal ptr_ring buffer is full. Instead, with this > > > > patch series, the associated netdev queue is stopped before this happens. > > > > This allows the connected qdisc to function correctly as reported by [1] > > > > and improves application-layer performance, see our paper [2]. Meanwhile > > > > the theoretical performance differs only slightly: > > > > > > > > > About this whole approach. > > > What if userspace is not consuming packets? > > > Won't the watchdog warnings appear? > > > Is it safe to allow userspace to block a tx queue > > > indefinitely? > > > > I think it's safe as it's a userspace device, there's no way to > > guarantee the userspace can process the packet in time (so no watchdog > > for TUN). > > > > Thanks > > Hmm. Anyway, I guess if we ever want to enable timeout for tun, > we can worry about it then. The problem is that the skb is freed until userspace calls recvmsg(), so it would be tricky to implement a watchdog. (Or if we can do, we can do BQL as well). > Does not need to block this patchset. Yes. Thanks > > > > > > > -- > > > MST > > > >
On Wed, Sep 24, 2025 at 04:08:33PM +0800, Jason Wang wrote: > On Wed, Sep 24, 2025 at 3:42 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > On Wed, Sep 24, 2025 at 03:33:08PM +0800, Jason Wang wrote: > > > On Wed, Sep 24, 2025 at 3:18 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > > > > > On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: > > > > > This patch series deals with TUN, TAP and vhost_net which drop incoming > > > > > SKBs whenever their internal ptr_ring buffer is full. Instead, with this > > > > > patch series, the associated netdev queue is stopped before this happens. > > > > > This allows the connected qdisc to function correctly as reported by [1] > > > > > and improves application-layer performance, see our paper [2]. Meanwhile > > > > > the theoretical performance differs only slightly: > > > > > > > > > > > > About this whole approach. > > > > What if userspace is not consuming packets? > > > > Won't the watchdog warnings appear? > > > > Is it safe to allow userspace to block a tx queue > > > > indefinitely? > > > > > > I think it's safe as it's a userspace device, there's no way to > > > guarantee the userspace can process the packet in time (so no watchdog > > > for TUN). > > > > > > Thanks > > > > Hmm. Anyway, I guess if we ever want to enable timeout for tun, > > we can worry about it then. > > The problem is that the skb is freed until userspace calls recvmsg(), > so it would be tricky to implement a watchdog. (Or if we can do, we > can do BQL as well). I thought the watchdog generally watches queues not individual skbs? > > Does not need to block this patchset. > > Yes. > > Thanks > > > > > > > > > > > -- > > > > MST > > > > > >
On Wed, Sep 24, 2025 at 4:10 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > On Wed, Sep 24, 2025 at 04:08:33PM +0800, Jason Wang wrote: > > On Wed, Sep 24, 2025 at 3:42 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > > > On Wed, Sep 24, 2025 at 03:33:08PM +0800, Jason Wang wrote: > > > > On Wed, Sep 24, 2025 at 3:18 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > > > > > > > On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: > > > > > > This patch series deals with TUN, TAP and vhost_net which drop incoming > > > > > > SKBs whenever their internal ptr_ring buffer is full. Instead, with this > > > > > > patch series, the associated netdev queue is stopped before this happens. > > > > > > This allows the connected qdisc to function correctly as reported by [1] > > > > > > and improves application-layer performance, see our paper [2]. Meanwhile > > > > > > the theoretical performance differs only slightly: > > > > > > > > > > > > > > > About this whole approach. > > > > > What if userspace is not consuming packets? > > > > > Won't the watchdog warnings appear? > > > > > Is it safe to allow userspace to block a tx queue > > > > > indefinitely? > > > > > > > > I think it's safe as it's a userspace device, there's no way to > > > > guarantee the userspace can process the packet in time (so no watchdog > > > > for TUN). > > > > > > > > Thanks > > > > > > Hmm. Anyway, I guess if we ever want to enable timeout for tun, > > > we can worry about it then. > > > > The problem is that the skb is freed until userspace calls recvmsg(), > > so it would be tricky to implement a watchdog. (Or if we can do, we > > can do BQL as well). > > I thought the watchdog generally watches queues not individual skbs? Yes, but only if ndo_tx_timeout is implemented. I mean it would be tricky if we want to implement ndo_tx_timeout since we can't choose a good timeout. Thanks
On Wed, Sep 24, 2025 at 04:30:45PM +0800, Jason Wang wrote: > On Wed, Sep 24, 2025 at 4:10 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > On Wed, Sep 24, 2025 at 04:08:33PM +0800, Jason Wang wrote: > > > On Wed, Sep 24, 2025 at 3:42 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > > > > > On Wed, Sep 24, 2025 at 03:33:08PM +0800, Jason Wang wrote: > > > > > On Wed, Sep 24, 2025 at 3:18 PM Michael S. Tsirkin <mst@redhat.com> wrote: > > > > > > > > > > > > On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: > > > > > > > This patch series deals with TUN, TAP and vhost_net which drop incoming > > > > > > > SKBs whenever their internal ptr_ring buffer is full. Instead, with this > > > > > > > patch series, the associated netdev queue is stopped before this happens. > > > > > > > This allows the connected qdisc to function correctly as reported by [1] > > > > > > > and improves application-layer performance, see our paper [2]. Meanwhile > > > > > > > the theoretical performance differs only slightly: > > > > > > > > > > > > > > > > > > About this whole approach. > > > > > > What if userspace is not consuming packets? > > > > > > Won't the watchdog warnings appear? > > > > > > Is it safe to allow userspace to block a tx queue > > > > > > indefinitely? > > > > > > > > > > I think it's safe as it's a userspace device, there's no way to > > > > > guarantee the userspace can process the packet in time (so no watchdog > > > > > for TUN). > > > > > > > > > > Thanks > > > > > > > > Hmm. Anyway, I guess if we ever want to enable timeout for tun, > > > > we can worry about it then. > > > > > > The problem is that the skb is freed until userspace calls recvmsg(), > > > so it would be tricky to implement a watchdog. (Or if we can do, we > > > can do BQL as well). > > > > I thought the watchdog generally watches queues not individual skbs? > > Yes, but only if ndo_tx_timeout is implemented. > > I mean it would be tricky if we want to implement ndo_tx_timeout since > we can't choose a good timeout. > > Thanks userspace could supply that, thinkably. anyway, we can worry about that when we need that. -- MST
On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: > This patch series deals with TUN, TAP and vhost_net which drop incoming > SKBs whenever their internal ptr_ring buffer is full. Instead, with this > patch series, the associated netdev queue is stopped before this happens. > This allows the connected qdisc to function correctly as reported by [1] > and improves application-layer performance, see our paper [2]. Meanwhile > the theoretical performance differs only slightly: > > +------------------------+----------+----------+ > | pktgen benchmarks | Stock | Patched | > | i5 6300HQ, 20M packets | | | > +------------------------+----------+----------+ > | TAP | 2.10Mpps | 1.99Mpps | > +------------------------+----------+----------+ > | TAP+vhost_net | 6.05Mpps | 6.14Mpps | > +------------------------+----------+----------+ > | Note: Patched had no TX drops at all, | > | while stock suffered numerous drops. | > +----------------------------------------------+ > > This patch series includes TUN, TAP, and vhost_net because they share > logic. Adjusting only one of them would break the others. Therefore, the > patch series is structured as follows: > 1+2: New ptr_ring helpers for 3 & 4 > 3: TUN & TAP: Stop netdev queue upon reaching a full ptr_ring so what happens if you only apply patches 1-3? > 4: TUN & TAP: Wake netdev queue after consuming an entry > 5+6+7: TUN & TAP: ptr_ring wrappers and other helpers to be called by > vhost_net > 8: vhost_net: Call the wrappers & helpers > > Possible future work: > - Introduction of Byte Queue Limits as suggested by Stephen Hemminger > - Adaption of the netdev queue flow control for ipvtap & macvtap > > [1] Link: > https://unix.stackexchange.com/questions/762935/traffic-shaping-ineffective-on-tun-device > [2] Link: > https://cni.etit.tu-dortmund.de/storages/cni-etit/r/Research/Publications/2025/Gebauer_2025_VTCFall/Gebauer_VTCFall2025_AuthorsVersion.pdf > > Links to previous versions: > V4: > https://lore.kernel.org/netdev/20250902080957.47265-1-simon.schippers@tu-dortmund.de/T/#u > V3: > https://lore.kernel.org/netdev/20250825211832.84901-1-simon.schippers@tu-dortmund.de/T/#u > V2: > https://lore.kernel.org/netdev/20250811220430.14063-1-simon.schippers@tu-dortmund.de/T/#u > V1: > https://lore.kernel.org/netdev/20250808153721.261334-1-simon.schippers@tu-dortmund.de/T/#u > > Changelog: > V4 -> V5: > - Stop the netdev queue prior to producing the final fitting ptr_ring entry > -> Ensures the consumer has the latest netdev queue state, making it safe > to wake the queue > -> Resolves an issue in vhost_net where the netdev queue could remain > stopped despite being empty > -> For TUN/TAP, the netdev queue no longer needs to be woken in the > blocking loop > -> Introduces new helpers __ptr_ring_full_next and > __ptr_ring_will_invalidate for this purpose > > - vhost_net now uses wrappers of TUN/TAP for ptr_ring consumption rather > than maintaining its own rx_ring pointer > > V3 -> V4: > - Target net-next instead of net > - Changed to patch series instead of single patch > - Changed to new title from old title > "TUN/TAP: Improving throughput and latency by avoiding SKB drops" > - Wake netdev queue with new helpers wake_netdev_queue when there is any > spare capacity in the ptr_ring instead of waiting for it to be empty > - Use tun_file instead of tun_struct in tun_ring_recv as a more consistent > logic > - Use smp_wmb() and smp_rmb() barrier pair, which avoids any packet drops > that happened rarely before > - Use safer logic for vhost_net using RCU read locks to access TUN/TAP data > > V2 -> V3: Added support for TAP and TAP+vhost_net. > > V1 -> V2: Removed NETDEV_TX_BUSY return case in tun_net_xmit and removed > unnecessary netif_tx_wake_queue in tun_ring_recv. > > Thanks, > Simon :) > > Simon Schippers (8): > __ptr_ring_full_next: Returns if ring will be full after next > insertion > Move the decision of invalidation out of __ptr_ring_discard_one > TUN, TAP & vhost_net: Stop netdev queue before reaching a full > ptr_ring > TUN & TAP: Wake netdev queue after consuming an entry > TUN & TAP: Provide ptr_ring_consume_batched wrappers for vhost_net > TUN & TAP: Provide ptr_ring_unconsume wrappers for vhost_net > TUN & TAP: Methods to determine whether file is TUN/TAP for vhost_net > vhost_net: Replace rx_ring with calls of TUN/TAP wrappers > > drivers/net/tap.c | 115 +++++++++++++++++++++++++++++++-- > drivers/net/tun.c | 136 +++++++++++++++++++++++++++++++++++---- > drivers/vhost/net.c | 90 +++++++++++++++++--------- > include/linux/if_tap.h | 15 +++++ > include/linux/if_tun.h | 18 ++++++ > include/linux/ptr_ring.h | 54 +++++++++++++--- > 6 files changed, 367 insertions(+), 61 deletions(-) > > -- > 2.43.0
On 23.09.25 16:55, Michael S. Tsirkin wrote: > On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: >> This patch series deals with TUN, TAP and vhost_net which drop incoming >> SKBs whenever their internal ptr_ring buffer is full. Instead, with this >> patch series, the associated netdev queue is stopped before this happens. >> This allows the connected qdisc to function correctly as reported by [1] >> and improves application-layer performance, see our paper [2]. Meanwhile >> the theoretical performance differs only slightly: >> >> +------------------------+----------+----------+ >> | pktgen benchmarks | Stock | Patched | >> | i5 6300HQ, 20M packets | | | >> +------------------------+----------+----------+ >> | TAP | 2.10Mpps | 1.99Mpps | >> +------------------------+----------+----------+ >> | TAP+vhost_net | 6.05Mpps | 6.14Mpps | >> +------------------------+----------+----------+ >> | Note: Patched had no TX drops at all, | >> | while stock suffered numerous drops. | >> +----------------------------------------------+ >> >> This patch series includes TUN, TAP, and vhost_net because they share >> logic. Adjusting only one of them would break the others. Therefore, the >> patch series is structured as follows: >> 1+2: New ptr_ring helpers for 3 & 4 >> 3: TUN & TAP: Stop netdev queue upon reaching a full ptr_ring > > > so what happens if you only apply patches 1-3? > The netdev queue of vhost_net would be stopped by tun_net_xmit but will never be woken again. >> 4: TUN & TAP: Wake netdev queue after consuming an entry >> 5+6+7: TUN & TAP: ptr_ring wrappers and other helpers to be called by >> vhost_net >> 8: vhost_net: Call the wrappers & helpers >> >> Possible future work: >> - Introduction of Byte Queue Limits as suggested by Stephen Hemminger >> - Adaption of the netdev queue flow control for ipvtap & macvtap >> >> [1] Link: >> https://unix.stackexchange.com/questions/762935/traffic-shaping-ineffective-on-tun-device >> [2] Link: >> https://cni.etit.tu-dortmund.de/storages/cni-etit/r/Research/Publications/2025/Gebauer_2025_VTCFall/Gebauer_VTCFall2025_AuthorsVersion.pdf >> >> Links to previous versions: >> V4: >> https://lore.kernel.org/netdev/20250902080957.47265-1-simon.schippers@tu-dortmund.de/T/#u >> V3: >> https://lore.kernel.org/netdev/20250825211832.84901-1-simon.schippers@tu-dortmund.de/T/#u >> V2: >> https://lore.kernel.org/netdev/20250811220430.14063-1-simon.schippers@tu-dortmund.de/T/#u >> V1: >> https://lore.kernel.org/netdev/20250808153721.261334-1-simon.schippers@tu-dortmund.de/T/#u >> >> Changelog: >> V4 -> V5: >> - Stop the netdev queue prior to producing the final fitting ptr_ring entry >> -> Ensures the consumer has the latest netdev queue state, making it safe >> to wake the queue >> -> Resolves an issue in vhost_net where the netdev queue could remain >> stopped despite being empty >> -> For TUN/TAP, the netdev queue no longer needs to be woken in the >> blocking loop >> -> Introduces new helpers __ptr_ring_full_next and >> __ptr_ring_will_invalidate for this purpose >> >> - vhost_net now uses wrappers of TUN/TAP for ptr_ring consumption rather >> than maintaining its own rx_ring pointer >> >> V3 -> V4: >> - Target net-next instead of net >> - Changed to patch series instead of single patch >> - Changed to new title from old title >> "TUN/TAP: Improving throughput and latency by avoiding SKB drops" >> - Wake netdev queue with new helpers wake_netdev_queue when there is any >> spare capacity in the ptr_ring instead of waiting for it to be empty >> - Use tun_file instead of tun_struct in tun_ring_recv as a more consistent >> logic >> - Use smp_wmb() and smp_rmb() barrier pair, which avoids any packet drops >> that happened rarely before >> - Use safer logic for vhost_net using RCU read locks to access TUN/TAP data >> >> V2 -> V3: Added support for TAP and TAP+vhost_net. >> >> V1 -> V2: Removed NETDEV_TX_BUSY return case in tun_net_xmit and removed >> unnecessary netif_tx_wake_queue in tun_ring_recv. >> >> Thanks, >> Simon :) >> >> Simon Schippers (8): >> __ptr_ring_full_next: Returns if ring will be full after next >> insertion >> Move the decision of invalidation out of __ptr_ring_discard_one >> TUN, TAP & vhost_net: Stop netdev queue before reaching a full >> ptr_ring >> TUN & TAP: Wake netdev queue after consuming an entry >> TUN & TAP: Provide ptr_ring_consume_batched wrappers for vhost_net >> TUN & TAP: Provide ptr_ring_unconsume wrappers for vhost_net >> TUN & TAP: Methods to determine whether file is TUN/TAP for vhost_net >> vhost_net: Replace rx_ring with calls of TUN/TAP wrappers >> >> drivers/net/tap.c | 115 +++++++++++++++++++++++++++++++-- >> drivers/net/tun.c | 136 +++++++++++++++++++++++++++++++++++---- >> drivers/vhost/net.c | 90 +++++++++++++++++--------- >> include/linux/if_tap.h | 15 +++++ >> include/linux/if_tun.h | 18 ++++++ >> include/linux/ptr_ring.h | 54 +++++++++++++--- >> 6 files changed, 367 insertions(+), 61 deletions(-) >> >> -- >> 2.43.0 >
On Wed, Sep 24, 2025 at 07:59:46AM +0200, Simon Schippers wrote: > On 23.09.25 16:55, Michael S. Tsirkin wrote: > > On Tue, Sep 23, 2025 at 12:15:45AM +0200, Simon Schippers wrote: > >> This patch series deals with TUN, TAP and vhost_net which drop incoming > >> SKBs whenever their internal ptr_ring buffer is full. Instead, with this > >> patch series, the associated netdev queue is stopped before this happens. > >> This allows the connected qdisc to function correctly as reported by [1] > >> and improves application-layer performance, see our paper [2]. Meanwhile > >> the theoretical performance differs only slightly: > >> > >> +------------------------+----------+----------+ > >> | pktgen benchmarks | Stock | Patched | > >> | i5 6300HQ, 20M packets | | | > >> +------------------------+----------+----------+ > >> | TAP | 2.10Mpps | 1.99Mpps | > >> +------------------------+----------+----------+ > >> | TAP+vhost_net | 6.05Mpps | 6.14Mpps | > >> +------------------------+----------+----------+ > >> | Note: Patched had no TX drops at all, | > >> | while stock suffered numerous drops. | > >> +----------------------------------------------+ > >> > >> This patch series includes TUN, TAP, and vhost_net because they share > >> logic. Adjusting only one of them would break the others. Therefore, the > >> patch series is structured as follows: > >> 1+2: New ptr_ring helpers for 3 & 4 > >> 3: TUN & TAP: Stop netdev queue upon reaching a full ptr_ring > > > > > > so what happens if you only apply patches 1-3? > > > > The netdev queue of vhost_net would be stopped by tun_net_xmit but will > never be woken again. So this breaks bisect. Don't split patches like this please. > >> 4: TUN & TAP: Wake netdev queue after consuming an entry > >> 5+6+7: TUN & TAP: ptr_ring wrappers and other helpers to be called by > >> vhost_net > >> 8: vhost_net: Call the wrappers & helpers > >> > >> Possible future work: > >> - Introduction of Byte Queue Limits as suggested by Stephen Hemminger > >> - Adaption of the netdev queue flow control for ipvtap & macvtap > >> > >> [1] Link: > >> https://unix.stackexchange.com/questions/762935/traffic-shaping-ineffective-on-tun-device > >> [2] Link: > >> https://cni.etit.tu-dortmund.de/storages/cni-etit/r/Research/Publications/2025/Gebauer_2025_VTCFall/Gebauer_VTCFall2025_AuthorsVersion.pdf > >> > >> Links to previous versions: > >> V4: > >> https://lore.kernel.org/netdev/20250902080957.47265-1-simon.schippers@tu-dortmund.de/T/#u > >> V3: > >> https://lore.kernel.org/netdev/20250825211832.84901-1-simon.schippers@tu-dortmund.de/T/#u > >> V2: > >> https://lore.kernel.org/netdev/20250811220430.14063-1-simon.schippers@tu-dortmund.de/T/#u > >> V1: > >> https://lore.kernel.org/netdev/20250808153721.261334-1-simon.schippers@tu-dortmund.de/T/#u > >> > >> Changelog: > >> V4 -> V5: > >> - Stop the netdev queue prior to producing the final fitting ptr_ring entry > >> -> Ensures the consumer has the latest netdev queue state, making it safe > >> to wake the queue > >> -> Resolves an issue in vhost_net where the netdev queue could remain > >> stopped despite being empty > >> -> For TUN/TAP, the netdev queue no longer needs to be woken in the > >> blocking loop > >> -> Introduces new helpers __ptr_ring_full_next and > >> __ptr_ring_will_invalidate for this purpose > >> > >> - vhost_net now uses wrappers of TUN/TAP for ptr_ring consumption rather > >> than maintaining its own rx_ring pointer > >> > >> V3 -> V4: > >> - Target net-next instead of net > >> - Changed to patch series instead of single patch > >> - Changed to new title from old title > >> "TUN/TAP: Improving throughput and latency by avoiding SKB drops" > >> - Wake netdev queue with new helpers wake_netdev_queue when there is any > >> spare capacity in the ptr_ring instead of waiting for it to be empty > >> - Use tun_file instead of tun_struct in tun_ring_recv as a more consistent > >> logic > >> - Use smp_wmb() and smp_rmb() barrier pair, which avoids any packet drops > >> that happened rarely before > >> - Use safer logic for vhost_net using RCU read locks to access TUN/TAP data > >> > >> V2 -> V3: Added support for TAP and TAP+vhost_net. > >> > >> V1 -> V2: Removed NETDEV_TX_BUSY return case in tun_net_xmit and removed > >> unnecessary netif_tx_wake_queue in tun_ring_recv. > >> > >> Thanks, > >> Simon :) > >> > >> Simon Schippers (8): > >> __ptr_ring_full_next: Returns if ring will be full after next > >> insertion > >> Move the decision of invalidation out of __ptr_ring_discard_one > >> TUN, TAP & vhost_net: Stop netdev queue before reaching a full > >> ptr_ring > >> TUN & TAP: Wake netdev queue after consuming an entry > >> TUN & TAP: Provide ptr_ring_consume_batched wrappers for vhost_net > >> TUN & TAP: Provide ptr_ring_unconsume wrappers for vhost_net > >> TUN & TAP: Methods to determine whether file is TUN/TAP for vhost_net > >> vhost_net: Replace rx_ring with calls of TUN/TAP wrappers > >> > >> drivers/net/tap.c | 115 +++++++++++++++++++++++++++++++-- > >> drivers/net/tun.c | 136 +++++++++++++++++++++++++++++++++++---- > >> drivers/vhost/net.c | 90 +++++++++++++++++--------- > >> include/linux/if_tap.h | 15 +++++ > >> include/linux/if_tun.h | 18 ++++++ > >> include/linux/ptr_ring.h | 54 +++++++++++++--- > >> 6 files changed, 367 insertions(+), 61 deletions(-) > >> > >> -- > >> 2.43.0 > >
© 2016 - 2025 Red Hat, Inc.