kactive_blk_num (K) is incremented on block close. last_kactive_blk_num (L)
is set to match K on block open and each timer. So the only time that they
differ is if a block is closed in tpacket_rcv and no new block could be
opened.
So the origin check L==K in timer callback only skip the case 'no new block
to open'. If we remove L==K check, it will make prb_curr_blk_in_use check
earlier, which will not cause any side effect.
Signed-off-by: Xin Zhao <jackzxcui1989@163.com>
---
net/packet/af_packet.c | 60 ++++++++++++++++++++----------------------
net/packet/internal.h | 6 -----
2 files changed, 28 insertions(+), 38 deletions(-)
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index a7017d7f0..d4eb4a4fe 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -669,7 +669,6 @@ static void init_prb_bdqc(struct packet_sock *po,
p1->knum_blocks = req_u->req3.tp_block_nr;
p1->hdrlen = po->tp_hdrlen;
p1->version = po->tp_version;
- p1->last_kactive_blk_num = 0;
po->stats.stats3.tp_freeze_q_cnt = 0;
if (req_u->req3.tp_retire_blk_tov)
p1->retire_blk_tov = req_u->req3.tp_retire_blk_tov;
@@ -693,7 +692,6 @@ static void _prb_refresh_rx_retire_blk_timer(struct tpacket_kbdq_core *pkc)
{
mod_timer(&pkc->retire_blk_timer,
jiffies + pkc->tov_in_jiffies);
- pkc->last_kactive_blk_num = pkc->kactive_blk_num;
}
/*
@@ -750,38 +748,36 @@ static void prb_retire_rx_blk_timer_expired(struct timer_list *t)
write_unlock(&pkc->blk_fill_in_prog_lock);
}
- if (pkc->last_kactive_blk_num == pkc->kactive_blk_num) {
- if (!frozen) {
- if (!BLOCK_NUM_PKTS(pbd)) {
- /* An empty block. Just refresh the timer. */
- goto refresh_timer;
- }
- prb_retire_current_block(pkc, po, TP_STATUS_BLK_TMO);
- if (!prb_dispatch_next_block(pkc, po))
- goto refresh_timer;
- else
- goto out;
+ if (!frozen) {
+ if (!BLOCK_NUM_PKTS(pbd)) {
+ /* An empty block. Just refresh the timer. */
+ goto refresh_timer;
+ }
+ prb_retire_current_block(pkc, po, TP_STATUS_BLK_TMO);
+ if (!prb_dispatch_next_block(pkc, po))
+ goto refresh_timer;
+ else
+ goto out;
+ } else {
+ /* Case 1. Queue was frozen because user-space was
+ * lagging behind.
+ */
+ if (prb_curr_blk_in_use(pbd)) {
+ /*
+ * Ok, user-space is still behind.
+ * So just refresh the timer.
+ */
+ goto refresh_timer;
} else {
- /* Case 1. Queue was frozen because user-space was
- * lagging behind.
+ /* Case 2. queue was frozen,user-space caught up,
+ * now the link went idle && the timer fired.
+ * We don't have a block to close.So we open this
+ * block and restart the timer.
+ * opening a block thaws the queue,restarts timer
+ * Thawing/timer-refresh is a side effect.
*/
- if (prb_curr_blk_in_use(pbd)) {
- /*
- * Ok, user-space is still behind.
- * So just refresh the timer.
- */
- goto refresh_timer;
- } else {
- /* Case 2. queue was frozen,user-space caught up,
- * now the link went idle && the timer fired.
- * We don't have a block to close.So we open this
- * block and restart the timer.
- * opening a block thaws the queue,restarts timer
- * Thawing/timer-refresh is a side effect.
- */
- prb_open_block(pkc, pbd);
- goto out;
- }
+ prb_open_block(pkc, pbd);
+ goto out;
}
}
diff --git a/net/packet/internal.h b/net/packet/internal.h
index 1e743d031..d367b9f93 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -24,12 +24,6 @@ struct tpacket_kbdq_core {
unsigned short kactive_blk_num;
unsigned short blk_sizeof_priv;
- /* last_kactive_blk_num:
- * trick to see if user-space has caught up
- * in order to avoid refreshing timer when every single pkt arrives.
- */
- unsigned short last_kactive_blk_num;
-
char *pkblk_start;
char *pkblk_end;
int kblk_size;
--
2.34.1On Sun, Aug 31, 2025 at 6:10 PM Xin Zhao <jackzxcui1989@163.com> wrote:
>
> kactive_blk_num (K) is incremented on block close. last_kactive_blk_num (L)
> is set to match K on block open and each timer. So the only time that they
> differ is if a block is closed in tpacket_rcv and no new block could be
> opened.
> So the origin check L==K in timer callback only skip the case 'no new block
> to open'. If we remove L==K check, it will make prb_curr_blk_in_use check
> earlier, which will not cause any side effect.
I believe the above commit message needs to be revised:
1) the above sentence (starting from 'if we remove L....') means
nothing because your modification doesn't change the behaviour when
the queue is not frozen.
2) lack of proofs/reasons on why exposing the prb_open_block() logic doesn't
cause side effects. It's the key proof that shows to future readers to
make sure this patch will not bring trouble.
>
> Signed-off-by: Xin Zhao <jackzxcui1989@163.com>
It was suggested by Willem, so please add:
Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
So far, it looks good to me as well:
Reviewed-by: Jason Xing <kerneljasonxing@gmail.com>
And I will finish reviewing the other patch by tomorrow :)
Thanks,
Jason
> ---
> net/packet/af_packet.c | 60 ++++++++++++++++++++----------------------
> net/packet/internal.h | 6 -----
> 2 files changed, 28 insertions(+), 38 deletions(-)
>
> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> index a7017d7f0..d4eb4a4fe 100644
> --- a/net/packet/af_packet.c
> +++ b/net/packet/af_packet.c
> @@ -669,7 +669,6 @@ static void init_prb_bdqc(struct packet_sock *po,
> p1->knum_blocks = req_u->req3.tp_block_nr;
> p1->hdrlen = po->tp_hdrlen;
> p1->version = po->tp_version;
> - p1->last_kactive_blk_num = 0;
> po->stats.stats3.tp_freeze_q_cnt = 0;
> if (req_u->req3.tp_retire_blk_tov)
> p1->retire_blk_tov = req_u->req3.tp_retire_blk_tov;
> @@ -693,7 +692,6 @@ static void _prb_refresh_rx_retire_blk_timer(struct tpacket_kbdq_core *pkc)
> {
> mod_timer(&pkc->retire_blk_timer,
> jiffies + pkc->tov_in_jiffies);
> - pkc->last_kactive_blk_num = pkc->kactive_blk_num;
> }
>
> /*
> @@ -750,38 +748,36 @@ static void prb_retire_rx_blk_timer_expired(struct timer_list *t)
> write_unlock(&pkc->blk_fill_in_prog_lock);
> }
>
> - if (pkc->last_kactive_blk_num == pkc->kactive_blk_num) {
> - if (!frozen) {
> - if (!BLOCK_NUM_PKTS(pbd)) {
> - /* An empty block. Just refresh the timer. */
> - goto refresh_timer;
> - }
> - prb_retire_current_block(pkc, po, TP_STATUS_BLK_TMO);
> - if (!prb_dispatch_next_block(pkc, po))
> - goto refresh_timer;
> - else
> - goto out;
> + if (!frozen) {
> + if (!BLOCK_NUM_PKTS(pbd)) {
> + /* An empty block. Just refresh the timer. */
> + goto refresh_timer;
> + }
> + prb_retire_current_block(pkc, po, TP_STATUS_BLK_TMO);
> + if (!prb_dispatch_next_block(pkc, po))
> + goto refresh_timer;
> + else
> + goto out;
> + } else {
> + /* Case 1. Queue was frozen because user-space was
> + * lagging behind.
> + */
> + if (prb_curr_blk_in_use(pbd)) {
> + /*
> + * Ok, user-space is still behind.
> + * So just refresh the timer.
> + */
> + goto refresh_timer;
> } else {
> - /* Case 1. Queue was frozen because user-space was
> - * lagging behind.
> + /* Case 2. queue was frozen,user-space caught up,
> + * now the link went idle && the timer fired.
> + * We don't have a block to close.So we open this
> + * block and restart the timer.
> + * opening a block thaws the queue,restarts timer
> + * Thawing/timer-refresh is a side effect.
> */
> - if (prb_curr_blk_in_use(pbd)) {
> - /*
> - * Ok, user-space is still behind.
> - * So just refresh the timer.
> - */
> - goto refresh_timer;
> - } else {
> - /* Case 2. queue was frozen,user-space caught up,
> - * now the link went idle && the timer fired.
> - * We don't have a block to close.So we open this
> - * block and restart the timer.
> - * opening a block thaws the queue,restarts timer
> - * Thawing/timer-refresh is a side effect.
> - */
> - prb_open_block(pkc, pbd);
> - goto out;
> - }
> + prb_open_block(pkc, pbd);
> + goto out;
> }
> }
>
> diff --git a/net/packet/internal.h b/net/packet/internal.h
> index 1e743d031..d367b9f93 100644
> --- a/net/packet/internal.h
> +++ b/net/packet/internal.h
> @@ -24,12 +24,6 @@ struct tpacket_kbdq_core {
> unsigned short kactive_blk_num;
> unsigned short blk_sizeof_priv;
>
> - /* last_kactive_blk_num:
> - * trick to see if user-space has caught up
> - * in order to avoid refreshing timer when every single pkt arrives.
> - */
> - unsigned short last_kactive_blk_num;
> -
> char *pkblk_start;
> char *pkblk_end;
> int kblk_size;
> --
> 2.34.1
>
>
Xin Zhao wrote: > kactive_blk_num (K) is incremented on block close. last_kactive_blk_num (L) > is set to match K on block open and each timer. So the only time that they > differ is if a block is closed in tpacket_rcv and no new block could be > opened. > So the origin check L==K in timer callback only skip the case 'no new block > to open'. If we remove L==K check, it will make prb_curr_blk_in_use check > earlier, which will not cause any side effect. > > Signed-off-by: Xin Zhao <jackzxcui1989@163.com> Reviewed-by: Willem de Bruijn <willemb@google.com>
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