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From: Nick Piggin <nickpiggin@yahoo.com.au>
To: "Ray Lee" <ray-lk@madrabbit.org>
Cc: "Peter Zijlstra" <peterz@infradead.org>,
	"Ingo Molnar" <mingo@elte.hu>,
	"LKML," <linux-kernel@vger.kernel.org>
Subject: Re: Poor PostgreSQL scaling on Linux 2.6.25-rc5 (vs 2.6.22)
Date: Mon, 17 Mar 2008 16:34:45 +1100	[thread overview]
Message-ID: <200803171634.46295.nickpiggin@yahoo.com.au> (raw)
In-Reply-To: <2c0942db0803162216r1892782bsc894d4188b51481b@mail.gmail.com>

On Monday 17 March 2008 16:16, Ray Lee wrote:
> On Sun, Mar 16, 2008 at 5:44 PM, Nick Piggin <nickpiggin@yahoo.com.au> 
wrote:
> >  I don't see how it is really helpful for interactive processes either.
> >  By definition, if they are not CPU bound, then they should be run
> >  quite soon after waking up; if they are CPU bound, then reducing
> >  efficiency by increasing context switches is effectively going to
> >  increase their latency anyway.
>
> How? Are you saying that switching the granularity to, say, 25ms, will
> *decrease* the latency of interactive tasks?

No. It shouldn't change them.


> And the efficiency we're talking about reducing here is due to the
> fact that tasks are hitting cold caches more times per second when the
> granularity is smaller, correct? Or are you concerned by another
> issue?

Secondary issues like the actual cost of context switch, but they are
generally in the noise compared to cache and tlb costs.


> > Can this be changed by default, please?
>
> Not without benchmarks of interactivity, please. There are far, far
> more linux desktops than there are servers. People expect to have to
> tune servers (I do, for the servers I maintain). People don't expect
> to have to tune a desktop to make it run well.

Linux desktops shouldn't run with massive loads anyway. Tuning the
scheduler to "work" well in an X session when you have a make -j100
in the background is retarded.

But sure, if the scheduler doesn't properly prioritize non-CPU bound
tasks versus CPU bound ones, then it should be fixed to do so.


  parent reply	other threads:[~2008-03-17  5:35 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-03-11  6:49 Nick Piggin
2008-03-11  7:58 ` Ingo Molnar
2008-03-11  8:28   ` Nick Piggin
2008-03-11  9:59     ` Ingo Molnar
2008-03-11 21:07 ` Nicholas Miell
2008-03-11 21:34   ` Cyrus Massoumi
2008-03-11 23:12     ` Nicholas Miell
2008-03-11 23:42       ` Nick Piggin
2008-03-11 23:47       ` Stephen Hemminger
2008-03-12  9:00       ` Zhang, Yanmin
     [not found] ` <20080311102538.GA30551@elte.hu>
     [not found]   ` <20080311120230.GA5386@elte.hu>
2008-03-12  1:21     ` Nick Piggin
2008-03-12  7:58       ` Peter Zijlstra
2008-03-17  0:44         ` Nick Piggin
2008-03-17  5:16           ` Ray Lee
2008-03-17  5:21             ` Willy Tarreau
2008-03-17  7:19               ` Nick Piggin
2008-03-17  8:26                 ` Willy Tarreau
2008-03-17  8:54                   ` Nick Piggin
2008-03-17  9:28                     ` Peter Zijlstra
2008-03-17  9:56                       ` Nick Piggin
2008-03-17 10:16                       ` Ingo Molnar
2008-03-17  5:34             ` Nick Piggin [this message]
2008-03-14 15:42 Xose Vazquez Perez

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