From: David Miller <davem@davemloft.net>
To: olteanv@gmail.com
Cc: kuba@kernel.org, netdev@vger.kernel.org, claudiu.manoil@nxp.com,
ioana.ciornei@nxp.com, Jiafei.Pan@nxp.com, yangbo.lu@nxp.com,
linux-kernel@vger.kernel.org, linux-rt-users@vger.kernel.org
Subject: Re: [PATCH net-next 2/2] enetc: use napi_schedule to be compatible with PREEMPT_RT
Date: Mon, 03 Aug 2020 18:21:45 -0700 (PDT) [thread overview]
Message-ID: <20200803.182145.2300252460016431673.davem@davemloft.net> (raw)
In-Reply-To: <20200803201009.613147-2-olteanv@gmail.com>
From: Vladimir Oltean <olteanv@gmail.com>
Date: Mon, 3 Aug 2020 23:10:09 +0300
> From: Jiafei Pan <Jiafei.Pan@nxp.com>
>
> The driver calls napi_schedule_irqoff() from a context where, in RT,
> hardirqs are not disabled, since the IRQ handler is force-threaded.
>
> In the call path of this function, __raise_softirq_irqoff() is modifying
> its per-CPU mask of pending softirqs that must be processed, using
> or_softirq_pending(). The or_softirq_pending() function is not atomic,
> but since interrupts are supposed to be disabled, nobody should be
> preempting it, and the operation should be safe.
>
> Nonetheless, when running with hardirqs on, as in the PREEMPT_RT case,
> it isn't safe, and the pending softirqs mask can get corrupted,
> resulting in softirqs being lost and never processed.
>
> To have common code that works with PREEMPT_RT and with mainline Linux,
> we can use plain napi_schedule() instead. The difference is that
> napi_schedule() (via __napi_schedule) also calls local_irq_save, which
> disables hardirqs if they aren't already. But, since they already are
> disabled in non-RT, this means that in practice we don't see any
> measurable difference in throughput or latency with this patch.
>
> Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Applied.
next prev parent reply other threads:[~2020-08-04 1:21 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-03 20:10 [PATCH net-next 1/2] dpaa2-eth: use napi_schedule to be compatible with PREEMPT_RT Vladimir Oltean
2020-08-03 20:10 ` [PATCH net-next 2/2] enetc: " Vladimir Oltean
2020-08-04 1:21 ` David Miller [this message]
2020-08-12 13:51 ` Sebastian Andrzej Siewior
2020-08-12 14:34 ` Vladimir Oltean
2020-08-12 15:13 ` Sebastian Andrzej Siewior
2020-08-24 10:59 ` Vladimir Oltean
2020-08-04 1:21 ` [PATCH net-next 1/2] dpaa2-eth: " David Miller
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200803.182145.2300252460016431673.davem@davemloft.net \
--to=davem@davemloft.net \
--cc=Jiafei.Pan@nxp.com \
--cc=claudiu.manoil@nxp.com \
--cc=ioana.ciornei@nxp.com \
--cc=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-rt-users@vger.kernel.org \
--cc=netdev@vger.kernel.org \
--cc=olteanv@gmail.com \
--cc=yangbo.lu@nxp.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).