linux-kernel - Re: RFC: futex_wait() can DoS the tick

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Message-ID: <1434031116.4051.18.camel@gmail.com>
Date:	Thu, 11 Jun 2015 15:58:36 +0200
From:	Mike Galbraith <umgwanakikbuti@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: RFC: futex_wait() can DoS the tick

On Thu, 2015-06-11 at 15:13 +0200, Thomas Gleixner wrote:

> What you are looking at is the actual timer interrupt vector, but
> that's not the the tick.
> 
> # grep 'expire_entry.*tick_sched_timer' trace2 | wc -l
> 45
> 
> 175 / 45  =~ 4 . So I you have CPNFIG_HZ=250
> 
> The kernel does not care whether the actual interrupt happens or the
> timer is expired by other means.

Learn something new every day.  I (obviously) had no idea that it's
perfectly fine for interrupts to go away when the CPU is busy.

Oh well.  Thanks for the new wrinkle in the mush between my ears.

	-Mike


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