linux-kernel - Re: [PATCH 0/5] Generic smp_call_function(), improvements, and smp_call_function

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Message-ID: <20080327123525.GN12346@kernel.dk>
Date:	Thu, 27 Mar 2008 13:35:25 +0100
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	linux-kernel@...r.kernel.org, npiggin@...e.de, paulus@...ba.org,
	tglx@...utronix.de, mingo@...hat.com, tony.luck@...el.com,
	Alan.Brunelle@...com
Subject: Re: [PATCH 0/5] Generic smp_call_function(), improvements, and  smp_call_function_single()

On Thu, Mar 27 2008, Ingo Molnar wrote:
> 
> * Jens Axboe <jens.axboe@...cle.com> wrote:
> 
> > > i'd love to be able to run/pull something simple that enables me to 
> > > replicate the measurements you did on a generic PC [without having 
> > > to hit any real IO hardware which would put any context switching 
> > > effects down into the noise category].
> > 
> > You can pull io-cpu-affinity or io-cpu-affinity-kthread from 
> > git://git.kernel.dk/linux-2.6-block.git - or just see the two attached 
> > patches, apply either one to current -git to test it.
> 
> another stupid question: what should i run in user-space to replicate 
> your "3 usecs versus 2 usecs" result? io-affinity-ipi.patch seems to 
> have no self-benchmarking capability at first sight. (I'd rather not try 
> and cook up anything myself - i'd like to reproduce the workload you 
> think is relevant for your IO affinity purposes.) Best would be to have 
> a Kconfig based self-test that just runs during bootup if i boot a 
> bzImage. (laziness rules - and this way i could also track performance 
> regressions more easily, by looking at historic serial logs.)

I didn't do those numbers - Alan, when you timed the kthread vs ipi
"wake up", what did you use? I'm guessing some hacked in test, perhaps
you can pass that to Ingo?

-- 
Jens Axboe

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