From: Ingo Molnar <mingo@kernel•org>
To: Christoph Lameter <cl@linux•com>
Cc: Tejun Heo <tj@kernel•org>,
akpm@linuxfoundation•org, Steven Rostedt <srostedt@redhat•com>,
linux-kernel@vger•kernel.org,
Peter Zijlstra <peterz@infradead•org>,
netdev@vger•kernel.org
Subject: Re: [pchecks v1 2/4] Use raw cpu ops for calls that would trigger with checks
Date: Tue, 24 Sep 2013 09:32:50 +0200 [thread overview]
Message-ID: <20130924073250.GD28538@gmail.com> (raw)
In-Reply-To: <000001414c3d064a-ebe0610b-6951-4a74-bd33-8480e3e1e364-000000@email.amazonses.com>
(netdev Cc:-ed)
* Christoph Lameter <cl@linux•com> wrote:
> These location triggered during testing with KVM.
>
> These are fetches without preemption off where we judged that
> to be more performance efficient or where other means of
> providing synchronization (BH handling) are available.
> Index: linux/include/net/snmp.h
> ===================================================================
> --- linux.orig/include/net/snmp.h 2013-09-12 13:26:29.216103951 -0500
> +++ linux/include/net/snmp.h 2013-09-12 13:26:29.208104037 -0500
> @@ -126,7 +126,7 @@ struct linux_xfrm_mib {
> extern __typeof__(type) __percpu *name[SNMP_ARRAY_SZ]
>
> #define SNMP_INC_STATS_BH(mib, field) \
> - __this_cpu_inc(mib[0]->mibs[field])
> + raw_cpu_inc(mib[0]->mibs[field])
>
> #define SNMP_INC_STATS_USER(mib, field) \
> this_cpu_inc(mib[0]->mibs[field])
> @@ -141,7 +141,7 @@ struct linux_xfrm_mib {
> this_cpu_dec(mib[0]->mibs[field])
>
> #define SNMP_ADD_STATS_BH(mib, field, addend) \
> - __this_cpu_add(mib[0]->mibs[field], addend)
> + raw_cpu_add(mib[0]->mibs[field], addend)
Are the networking folks fine with allowing unafe operations of SNMP stats
in preemptible sections, or should the kernel produce an optional warning
message if CONFIG_PREEMPT_DEBUG=y and these ops are used in preemptible
(non-bh, non-irq-handler, non-irqs-off, etc.) sections?
RAW_SNMP_*_STATS() ops could be used to annotate those places where that
kind of usage is safe.
Thanks,
Ingo
next parent reply other threads:[~2013-09-24 7:32 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20130923191256.584672290@linux.com>
[not found] ` <000001414c3d064a-ebe0610b-6951-4a74-bd33-8480e3e1e364-000000@email.amazonses.com>
2013-09-24 7:32 ` Ingo Molnar [this message]
2013-09-24 12:45 ` [pchecks v1 2/4] Use raw cpu ops for calls that would trigger with checks Eric Dumazet
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