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net: napi: Skip last poll when arming gro timer in busy poll

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Skip the extra call to napi->poll(), if the gro timer is armed at the
end of busy polling. This removes the need for having a separate
__busy_poll_stop() routine and its code is moved directly into the
relevant places in busy_poll_stop(). Remove obsolete comment about
ndo_busy_poll_stop().

This is a follow-up to commit 58e2330bd4 ("net: napi: Avoid gro timer
misfiring at end of busypoll"), which has deferred arming the gro timer
to the end of __busy_poll_stop() to eliminate a race condition between
a short timer and long poll that could leave the queue stuck with
interrupts disabled and no timer armed.

Co-developed-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Signed-off-by: Martin Karsten <mkarsten@uwaterloo.ca>
Link: https://patch.msgid.link/20260523012247.1574691-1-mkarsten@uwaterloo.ca
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Martin Karsten 2026-05-22 21:22:20 -04:00 committed by Jakub Kicinski
parent 29fb4a2641
commit 7599c13dbe
1 changed files with 27 additions and 35 deletions
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62
net/core/dev.c
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@ -6863,22 +6863,6 @@ static void skb_defer_free_flush(void)
#if defined(CONFIG_NET_RX_BUSY_POLL)
static void __busy_poll_stop(struct napi_struct *napi, unsigned long timeout)
{
if (!timeout) {
gro_normal_list(&napi->gro);
__napi_schedule(napi);
return;
}
/* Flush too old packets. If HZ < 1000, flush all packets */
gro_flush_normal(&napi->gro, HZ >= 1000);
clear_bit(NAPI_STATE_SCHED, &napi->state);
hrtimer_start(&napi->timer, ns_to_ktime(timeout),
HRTIMER_MODE_REL_PINNED);
}
enum {
NAPI_F_PREFER_BUSY_POLL = 1,
NAPI_F_END_ON_RESCHED = 2,
@ -6894,8 +6878,8 @@ static void busy_poll_stop(struct napi_struct *napi, void *have_poll_lock,
/* Busy polling means there is a high chance device driver hard irq
* could not grab NAPI_STATE_SCHED, and that NAPI_STATE_MISSED was
* set in napi_schedule_prep().
* Since we are about to call napi->poll() once more, we can safely
* clear NAPI_STATE_MISSED.
* Since we either call napi->poll() once more or start the timer,
* we can safely clear NAPI_STATE_MISSED.
*
* Note: x86 could use a single "lock and ..." instruction
* to perform these two clear_bit()
@ -6908,27 +6892,35 @@ static void busy_poll_stop(struct napi_struct *napi, void *have_poll_lock,
if (flags & NAPI_F_PREFER_BUSY_POLL) {
napi->defer_hard_irqs_count = napi_get_defer_hard_irqs(napi);
if (napi->defer_hard_irqs_count) {
/* A short enough gro flush timeout and long enough
* poll can result in timer firing too early.
* Timer will be armed later if necessary.
*/
if (napi->defer_hard_irqs_count)
timeout = napi_get_gro_flush_timeout(napi);
}
if (timeout) {
netpoll_poll_unlock(have_poll_lock);
/* Drain aged GRO packets before clearing SCHED since the NAPI
* won't run again until after the timer fires. When HZ < 1000,
* GRO age comparison is too coarse, so flush everything.
*/
gro_flush_normal(&napi->gro, HZ >= 1000);
clear_bit(NAPI_STATE_SCHED, &napi->state);
hrtimer_start(&napi->timer, ns_to_ktime(timeout),
HRTIMER_MODE_REL_PINNED);
} else {
/* Use driver poll to re-enable device interrupts. */
rc = napi->poll(napi, budget);
/* Unless rc == budget we no longer own the NAPI instance,
* IRQ may fire on another CPU, poll this NAPI, and enter GRO.
*/
trace_napi_poll(napi, rc, budget);
netpoll_poll_unlock(have_poll_lock);
if (rc == budget) {
gro_normal_list(&napi->gro);
__napi_schedule(napi);
}
}
/* All we really want here is to re-enable device interrupts.
* Ideally, a new ndo_busy_poll_stop() could avoid another round.
*/
rc = napi->poll(napi, budget);
/* We can't gro_normal_list() here, because napi->poll() might have
* rearmed the napi (napi_complete_done()) in which case it could
* already be running on another CPU.
*/
trace_napi_poll(napi, rc, budget);
netpoll_poll_unlock(have_poll_lock);
if (rc == budget)
__busy_poll_stop(napi, timeout);
bpf_net_ctx_clear(bpf_net_ctx);
local_bh_enable();
}