From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Christoph Lameter <cl@linux.com>, Tejun Heo <tj@kernel.org>,
akpm@linuxfoundation.org, Eric Dumazet <edumazet@google.com>,
netdev@vger.kernel.org, Steven Rostedt <srostedt@redhat.com>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [raw v1 2/4] [NET] Use raw_cpu ops for SNMP stats
Date: Tue, 8 Oct 2013 12:21:42 +0200 [thread overview]
Message-ID: <20131008102142.GT3081@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20131008072114.GA4455@gmail.com>
On Tue, Oct 08, 2013 at 09:21:14AM +0200, Ingo Molnar wrote:
>
> * Christoph Lameter <cl@linux.com> wrote:
>
> > SNMP stats are not protected by preemption but by bh handling.
>
> Most forms of bh exclusion work via the preemption count though, and
> softirq contexts themselves are generally not preemptible [to other CPUs]
> either.
>
> So the warnings should, in most cases, not trigger.
Right, so softirqs run either in the irq tail at which point
preempt_count += SOFTIRQ_OFFSET and thus preemption is disabled, or it
runs in ksoftirqd which has strict cpu affinity which also disables the
warning, and it also increments preempt_count with SOFTIRQ_OFFSET to
exclude the softirq from interrupts while its running, also disabling
the warning.
So it should very much not trigger.. if it does you want to know about
it.
next prev parent reply other threads:[~2013-10-08 10:22 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20131007183226.334180014@linux.com>
2013-10-07 18:31 ` [raw v1 1/4] Use raw_cpu ops for determining current NUMA node Christoph Lameter
2013-10-07 18:31 ` [raw v1 2/4] [NET] Use raw_cpu ops for SNMP stats Christoph Lameter
2013-10-08 7:21 ` Ingo Molnar
2013-10-08 10:21 ` Peter Zijlstra [this message]
2013-10-08 10:26 ` Ingo Molnar
2013-10-07 18:32 ` [raw v1 3/4] Use raw_cpu_write for initialization of per cpu refcount Christoph Lameter
2013-10-07 18:32 ` [raw v1 4/4] net: __this_cpu_inc in route.c Christoph Lameter
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