From: Ingo Molnar <mingo@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
Kautuk Consul <consul.kautuk@gmail.com>,
Ingo Molnar <mingo@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Michal Hocko <mhocko@suse.cz>,
David Rientjes <rientjes@google.com>,
Ionut Alexa <ionut.m.alexa@gmail.com>,
Guillaume Morin <guillaume@morinfr.org>,
linux-kernel@vger.kernel.org, Kirill Tkhai <tkhai@yandex.ru>
Subject: Re: [PATCH 1/1] do_exit(): Solve possibility of BUG() due to race with try_to_wake_up()
Date: Thu, 4 Sep 2014 07:04:24 +0200 [thread overview]
Message-ID: <20140904050424.GA26756@gmail.com> (raw)
In-Reply-To: <20140903144450.GB7083@twins.programming.kicks-ass.net>
* Peter Zijlstra <peterz@infradead.org> wrote:
> > Ah, I simply do not know what is cheaper, even on x86. Well,
> > we need to enable/disable irqs, but again I do not really
> > know how much does this cost.
>
> Ah good point about that IRQ thing, yes that's horribly
> expensive.
Enabling/disabling local IRQs is not really expensive (it's a
flat cost essentially - below 10 cycles on modern x86 CPUs) -
especially if we consider the 100x-1000x frequency difference
between schedule() and exit(), on typical systems:
$ grep -E 'ctxt|processes' /proc/stat
ctxt 47166536
processes 91876
And that's from a system that emphatically does not schedule
much. On others the difference is much larger.
So please don't push complexity into the scheduler from
lower-freq areas of the kernel!
Thanks,
Ingo
next prev parent reply other threads:[~2014-09-04 5:04 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-25 10:54 [PATCH 1/1] do_exit(): Solve possibility of BUG() due to race with try_to_wake_up() Kautuk Consul
2014-08-25 15:57 ` Oleg Nesterov
2014-08-26 4:45 ` Kautuk Consul
2014-08-26 15:03 ` Oleg Nesterov
2014-09-01 15:39 ` Peter Zijlstra
2014-09-01 17:58 ` Oleg Nesterov
2014-09-01 19:09 ` Peter Zijlstra
2014-09-02 15:52 ` Oleg Nesterov
2014-09-02 16:47 ` Oleg Nesterov
2014-09-02 17:39 ` Peter Zijlstra
2014-09-03 13:36 ` Oleg Nesterov
2014-09-03 14:44 ` Peter Zijlstra
2014-09-03 15:18 ` Oleg Nesterov
2014-09-04 7:15 ` Peter Zijlstra
2014-09-04 17:03 ` Paul E. McKenney
2014-09-04 5:04 ` Ingo Molnar [this message]
2014-09-04 6:32 ` Peter Zijlstra
2014-09-03 16:08 ` task_numa_fault() && TASK_DEAD Oleg Nesterov
2014-09-03 16:33 ` Rik van Riel
2014-09-04 7:11 ` Peter Zijlstra
2014-09-04 10:39 ` Oleg Nesterov
2014-09-04 19:14 ` Hugh Dickins
2014-09-05 11:35 ` Oleg Nesterov
2014-09-03 9:04 ` [PATCH 1/1] do_exit(): Solve possibility of BUG() due to race with try_to_wake_up() Kirill Tkhai
2014-09-03 9:45 ` Peter Zijlstra
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