From: Clark Williams <clrkwllms@kernel.org>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: wen.yang@linux.dev, Steven Rostedt <rostedt@goodmis.org>,
Eric Dumazet <edumazet@google.com>,
Jesper Dangaard Brouer <brouer@redhat.com>,
Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
linux-rt-devel@list.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6.1-rt 00/15] net: Backport backlog-NAPI threads to resolve PREEMPT_RT softirq warning in SMP flush
Date: Thu, 15 Oct 2026 08:34:28 -0500 [thread overview]
Message-ID: <atDWZDywit4ilzJ8@demetrius> (raw)
In-Reply-To: <20261014150853.f8I2fNx0@linutronix.de>
On Wed, Oct 14, 2026 at 05:08:53PM +0200, Sebastian Andrzej Siewior wrote:
> Please keep the networking folks out of the loop. This is a backport
> request which goes entirely via the RT-queue.
>
> On 2026-10-14 01:58:34 [+0800], wen.yang@linux.dev wrote:
> > From: Wen Yang <wen.yang@linux.dev>
> >
> > *** Overview ***
> > Backport the backlog-NAPI smpboot-thread mechanism and its prerequisite
> > NAPI/RPS/defer_list work from upstream (v6.4 - v6.9) to v6.1-rt-next.
> >
> > *** Problem ***
> > On PREEMPT_RT, RPS steers packets to a remote CPU's backlog by sending an
> > IPI. The IPI handler (rps_trigger_softirq) calls ____napi_schedule(), which
> > raises NET_RX_SOFTIRQ. do_softirq_post_smp_call_flush() then sees a softirq
> > pending that was not pending before the flush, and NET_RX_SOFTIRQ is not
> > masked by SCHED_SOFTIRQ_MASK, so it fires:
>
> I was about to point out that v6.1-RT should have duct tape for this but
> from reading 1/15 is see that this duct is not complete and is missing
> RPS. Indeed.
>
> A backport of what is merged is my preference, too. However, we should
> get v6.6-rt fixed first then v6.1-rt. Otherwise users upgrading from
> v6.1 to v6.6 will have this case broken.
>
> Clark, any objections here from your side?
>
> Sebastian
I don't have a fundamental objection to the backport and agree we should
do v6.6-rt first, then move that back to v6.1-rt.
So it sounds like we need to pull in the RPS code first?
Clark
--
The United States Coast Guard
Ruining Natural Selection since 1790
prev parent reply other threads:[~2026-10-15 13:34 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-13 17:58 wen.yang
2026-10-13 17:58 ` [PATCH 01/15] Revert "net: Avoid the IPI to free the" wen.yang
2026-10-13 17:58 ` [PATCH 02/15] net: avoid irqsave in skb_defer_free_flush wen.yang
2026-10-13 17:58 ` [PATCH 03/15] net: napi_schedule_rps() cleanup wen.yang
2026-10-13 17:58 ` [PATCH 04/15] net: add softnet_data.in_net_rx_action wen.yang
2026-10-13 17:58 ` [PATCH 05/15] net: optimize napi_schedule_rps() wen.yang
2026-10-13 17:58 ` [PATCH 06/15] net: optimize ____napi_schedule() to avoid extra NET_RX_SOFTIRQ wen.yang
2026-10-13 17:58 ` [PATCH 07/15] net: add debugging checks in skb_attempt_defer_free() wen.yang
2026-10-13 17:58 ` [PATCH 08/15] net: do not provide hard irq safety for sd->defer_lock wen.yang
2026-10-13 17:58 ` [PATCH 09/15] net: move skb_defer_free_flush() up wen.yang
2026-10-13 18:02 ` [PATCH 10/15] net: make napi_threaded_poll() aware of sd->defer_list wen.yang
2026-10-13 18:02 ` [PATCH 11/15] net: optimize napi_threaded_poll() vs RPS/RFS wen.yang
2026-10-13 18:02 ` [PATCH 12/15] net: Remove conditional threaded-NAPI wakeup based on task state wen.yang
2026-10-13 18:02 ` [PATCH 13/15] net: Use backlog-NAPI to clean up the defer_list wen.yang
2026-10-13 18:02 ` [PATCH 14/15] net: Allow to use SMP threads for backlog NAPI wen.yang
2026-10-13 18:02 ` [PATCH 15/15] net: Rename rps_lock to backlog_lock wen.yang
2026-10-14 15:08 ` [PATCH v6.1-rt 00/15] net: Backport backlog-NAPI threads to resolve PREEMPT_RT softirq warning in SMP flush Sebastian Andrzej Siewior
2026-10-15 13:34 ` Clark Williams [this message]
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