This is a rebase of patches that Rich Jones first posted in 2023:
https://lists.gnu.org/archive/html/qemu-devel/2023-03/msg03320.html

I'm still leaving the series in an RFC state while I'm trying to
improve the code to better play with all of the multi-queue changes in
the block layer in the meantime.  In my own testing, the patches as
presented here are not making any noticeable difference in qemu-img
convert to a local destination file (multi-conn=1 was not much
different than multi-conn=4, although I did validate that multiple
sockets were in use and the round robin code was working).  Other
benchmarks did show improvements, such as qemu convert targeting an
nbdkit server on a curl backend getting a 20% boost when I ramped
multi-conn from 1 to 4.

I have more patches on top of these to post to the list once I can get
benchmark numbers that make more sense.

Richard W.M. Jones (4):
  nbd: Add multi-conn option
  nbd: Split out block device state from underlying NBD connections
  nbd: Open multiple NBD connections if multi-conn is set
  nbd: Enable multi-conn using round-robin

 qapi/block-core.json |   8 +-
 block/coroutines.h   |   5 +-
 block/nbd.c          | 796 +++++++++++++++++++++++++------------------
 3 files changed, 479 insertions(+), 330 deletions(-)

-- 
2.49.0

> This is a rebase of patches that Rich Jones first posted in 2023:
 > https://lists.gnu.org/archive/html/qemu-devel/2023-03/msg03320.html
>
> I'm still leaving the series in an RFC state while I'm trying to
> improve the code to better play with all of the multi-queue changes in
> the block layer in the meantime.  In my own testing, the patches as
> presented here are not making any noticeable difference in qemu-img
> convert to a local destination file (multi-conn=1 was not much
> different than multi-conn=4, although I did validate that multiple
> sockets were in use and the round robin code was working).  Other
> benchmarks did show improvements, such as qemu convert targeting an
> nbdkit server on a curl backend getting a 20% boost when I ramped
> multi-conn from 1 to 4.
>
> I have more patches on top of these to post to the list once I can get
> benchmark numbers that make more sense.
> 
> Richard W.M. Jones (4):
>   nbd: Add multi-conn option
>   nbd: Split out block device state from underlying NBD connections
>   nbd: Open multiple NBD connections if multi-conn is set
>   nbd: Enable multi-conn using round-robin
> 
>  qapi/block-core.json |   8 +-
>  block/coroutines.h   |   5 +-
>  block/nbd.c          | 796 +++++++++++++++++++++++++------------------
>  3 files changed, 479 insertions(+), 330 deletions(-)

This series makes my day.

I have a request from our partners to implement exactly this feature
to improve the backup restoration performance in their scenario.
The case is the following
+---------+  +----------+              +----------+  +------+
| Storage |->|IPsec gate|...Internet...|IPsec gate|->|Target|
+---------+  +----------+              +----------+  +------+
In this case the performance could be limited not by the Internet
of something else, but with the raw CPU performance in VMs which
are doing encryption/decryption.

I was specifically requested to implement multi-conn inside QEMU
client, which was used to run the system from the backup while
restoration is performed.

This makes a lot of sense for me even if there is no direct benefit
without bottleneck in the middle.

Thank you in advance,
	Den

On Mon, Apr 28, 2025 at 01:46:43PM -0500, Eric Blake wrote:
> This is a rebase of patches that Rich Jones first posted in 2023:
> https://lists.gnu.org/archive/html/qemu-devel/2023-03/msg03320.html
> 
> I'm still leaving the series in an RFC state while I'm trying to
> improve the code to better play with all of the multi-queue changes in
> the block layer in the meantime.  In my own testing, the patches as
> presented here are not making any noticeable difference in qemu-img
> convert to a local destination file (multi-conn=1 was not much
> different than multi-conn=4, although I did validate that multiple
> sockets were in use and the round robin code was working).  Other
> benchmarks did show improvements, such as qemu convert targeting an
> nbdkit server on a curl backend getting a 20% boost when I ramped
> multi-conn from 1 to 4.
>
> I have more patches on top of these to post to the list once I can get
> benchmark numbers that make more sense.

I'm curious if you are benchmarking UNIX or TCP sockets ?

If UNIX sockets, then that recent patch about increasing socket buffer
size for UNIX sockets rings alarm bells. ie, I wonder if the artificially
low UNIX socket buf size on Linux is preventing you seeing any significant
multi-conn benefits ?

IOW, add that socket buf size patch on top of this series, before
benchmarking again ?

> 
> Richard W.M. Jones (4):
>   nbd: Add multi-conn option
>   nbd: Split out block device state from underlying NBD connections
>   nbd: Open multiple NBD connections if multi-conn is set
>   nbd: Enable multi-conn using round-robin
> 
>  qapi/block-core.json |   8 +-
>  block/coroutines.h   |   5 +-
>  block/nbd.c          | 796 +++++++++++++++++++++++++------------------
>  3 files changed, 479 insertions(+), 330 deletions(-)

With regards,
Daniel
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