From: Jakub Kicinski <kuba@kernel•org>
To: Joe Damato <jdamato@fastly•com>
Cc: netdev@vger•kernel.org, corbet@lwn•net, hdanton@sina•com,
bagasdotme@gmail•com, pabeni@redhat•com, namangulati@google•com,
edumazet@google•com, amritha.nambiar@intel•com,
sridhar.samudrala@intel•com, sdf@fomichev•me, peter@typeblog•net,
m2shafiei@uwaterloo•ca, bjorn@rivosinc•com, hch@infradead•org,
willy@infradead•org, willemdebruijn.kernel@gmail•com,
skhawaja@google•com, Martin Karsten <mkarsten@uwaterloo•ca>,
"David S. Miller" <davem@davemloft•net>,
Simon Horman <horms@kernel•org>, David Ahern <dsahern@kernel•org>,
Sebastian Andrzej Siewior <bigeasy@linutronix•de>,
Lorenzo Bianconi <lorenzo@kernel•org>,
Alexander Lobakin <aleksander.lobakin@intel•com>,
linux-kernel@vger•kernel.org (open list)
Subject: Re: [PATCH net-next v6 2/7] net: Suspend softirq when prefer_busy_poll is set
Date: Tue, 5 Nov 2024 21:03:38 -0800 [thread overview]
Message-ID: <20241105210338.5364375d@kernel.org> (raw)
In-Reply-To: <20241104215542.215919-3-jdamato@fastly.com>
On Mon, 4 Nov 2024 21:55:26 +0000 Joe Damato wrote:
> From: Martin Karsten <mkarsten@uwaterloo•ca>
>
> When NAPI_F_PREFER_BUSY_POLL is set during busy_poll_stop and the
> irq_suspend_timeout is nonzero, this timeout is used to defer softirq
> scheduling, potentially longer than gro_flush_timeout. This can be used
> to effectively suspend softirq processing during the time it takes for
> an application to process data and return to the next busy-poll.
>
> The call to napi->poll in busy_poll_stop might lead to an invocation of
The call to napi->poll when we're arming the timer is counter
productive, right? Maybe we can take this opportunity to add
the seemingly missing logic to skip over it?
> napi_complete_done, but the prefer-busy flag is still set at that time,
> so the same logic is used to defer softirq scheduling for
> irq_suspend_timeout.
>
> Signed-off-by: Martin Karsten <mkarsten@uwaterloo•ca>
> Co-developed-by: Joe Damato <jdamato@fastly•com>
> Signed-off-by: Joe Damato <jdamato@fastly•com>
> Tested-by: Joe Damato <jdamato@fastly•com>
> Tested-by: Martin Karsten <mkarsten@uwaterloo•ca>
> Acked-by: Stanislav Fomichev <sdf@fomichev•me>
> Reviewed-by: Sridhar Samudrala <sridhar.samudrala@intel•com>
> ---
> v3:
> - Removed reference to non-existent sysfs parameter from commit
> message. No functional/code changes.
>
> net/core/dev.c | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 4d910872963f..51d88f758e2e 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6239,7 +6239,12 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
> timeout = napi_get_gro_flush_timeout(n);
> n->defer_hard_irqs_count = napi_get_defer_hard_irqs(n);
> }
> - if (n->defer_hard_irqs_count > 0) {
> + if (napi_prefer_busy_poll(n)) {
> + timeout = napi_get_irq_suspend_timeout(n);
Why look at the suspend timeout in napi_complete_done()?
We are unlikely to be exiting busy poll here.
Is it because we need more time than gro_flush_timeout
for the application to take over the polling?
> + if (timeout)
> + ret = false;
> + }
> + if (ret && n->defer_hard_irqs_count > 0) {
> n->defer_hard_irqs_count--;
> timeout = napi_get_gro_flush_timeout(n);
> if (timeout)
> @@ -6375,9 +6380,13 @@ static void busy_poll_stop(struct napi_struct *napi, void *have_poll_lock,
> bpf_net_ctx = bpf_net_ctx_set(&__bpf_net_ctx);
>
> if (flags & NAPI_F_PREFER_BUSY_POLL) {
> - napi->defer_hard_irqs_count = napi_get_defer_hard_irqs(napi);
> - timeout = napi_get_gro_flush_timeout(napi);
> - if (napi->defer_hard_irqs_count && timeout) {
> + timeout = napi_get_irq_suspend_timeout(napi);
Even here I'm not sure if we need to trigger suspend.
I don't know the eventpoll code well but it seems like you suspend
and resume based on events when exiting epoll. Why also here?
> + if (!timeout) {
> + napi->defer_hard_irqs_count = napi_get_defer_hard_irqs(napi);
> + if (napi->defer_hard_irqs_count)
> + timeout = napi_get_gro_flush_timeout(napi);
> + }
> + if (timeout) {
> hrtimer_start(&napi->timer, ns_to_ktime(timeout), HRTIMER_MODE_REL_PINNED);
> skip_schedule = true;
> }
next prev parent reply other threads:[~2024-11-06 5:03 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-04 21:55 [PATCH net-next v6 0/7] Suspend IRQs during application busy periods Joe Damato
2024-11-04 21:55 ` [PATCH net-next v6 1/7] net: Add napi_struct parameter irq_suspend_timeout Joe Damato
2024-11-04 21:55 ` [PATCH net-next v6 2/7] net: Suspend softirq when prefer_busy_poll is set Joe Damato
2024-11-06 5:03 ` Jakub Kicinski [this message]
2024-11-06 16:52 ` Joe Damato
2024-11-06 23:31 ` Jakub Kicinski
2024-11-07 3:24 ` Joe Damato
2024-11-07 21:01 ` Joe Damato
2024-11-08 3:52 ` Jakub Kicinski
2024-11-04 21:55 ` [PATCH net-next v6 3/7] net: Add control functions for irq suspension Joe Damato
2024-11-04 21:55 ` [PATCH net-next v6 4/7] eventpoll: Trigger napi_busy_loop, if prefer_busy_poll is set Joe Damato
2024-11-04 21:55 ` [PATCH net-next v6 5/7] eventpoll: Control irq suspension for prefer_busy_poll Joe Damato
2024-11-04 21:55 ` [PATCH net-next v6 6/7] selftests: net: Add busy_poll_test Joe Damato
2024-11-05 3:50 ` Stanislav Fomichev
2024-11-05 17:49 ` Joe Damato
2024-11-04 21:55 ` [PATCH net-next v6 7/7] docs: networking: Describe irq suspension Joe Damato
2024-11-05 1:12 ` Bagas Sanjaya
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