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Date: Wed, 22 Apr 2015 17:29:40 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
        viresh kumar <viresh.kumar@linaro.org>, Ingo Molnar <mingo@redhat.com>,
        linaro-kernel@lists.linaro.org, linux-kernel@vger.kernel.org,
        Steven Miao <realmz6@gmail.com>, shashim@codeaurora.org
Subject: Re: [PATCH 1/2] timer: Avoid waking up an idle-core by migrate
 running timer
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On Tue, Apr 21, 2015 at 02:54:55PM -0700, Eric Dumazet wrote:
> On Tue, 2015-04-21 at 23:32 +0200, Thomas Gleixner wrote:
> 
> > 
> > Are you realizing that __mod_timer() is a massive hotpath for network
> > heavy workloads?
> 
> BTW I was considering using mod_timer_pinned() from these networking
> timers (ie sk_reset_timer())
> 
> get_nohz_timer_target() sounds cool for laptop users, but is one cause
> for bad responses to DDOS, when the selected cpu gets stressed.
> 
> This is the reason I used mod_timer_pinned() in commit 789f558cfb3680ae
> ("tcp/dccp: get rid of central timewait timer")

Hmm, that sounds unfortunate, this would wreck life for the power aware
laptop/tablet etc.. people.

There is already a sysctl to manage this, is that not enough to mitigate
this problem on the server side of things?