Message-ID: <3F2F26BA.3060904@cyberone.com.au>
Date: Tue, 05 Aug 2003 13:38:34 +1000
From: Nick Piggin <piggin@cyberone.com.au>
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To: William Lee Irwin III <wli@holomorphy.com>
CC: Marc-Christian Petersen <m.c.p@wolk-project.de>,
       Felipe Alfaro Solana <felipe_alfaro@linuxmail.org>,
       Con Kolivas <kernel@kolivas.org>,
       linux kernel mailing list <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH] O11int for interactivity
References: <200307301038.49869.kernel@kolivas.org> <20030802225513.GE32488@holomorphy.com> <200308030119.47474.m.c.p@wolk-project.de> <200308042106.51676.m.c.p@wolk-project.de> <20030804195335.GK32488@holomorphy.com> <3F2F00B0.9050804@cyberone.com.au> <20030805024103.GM32488@holomorphy.com> <3F2F1F80.7060207@cyberone.com.au> <20030805031341.GN32488@holomorphy.com> <3F2F231C.3030901@cyberone.com.au> <20030805033119.GO32488@holomorphy.com>
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William Lee Irwin III wrote:

>William Lee Irwin III wrote:
>
>>>Well, I was vaguely hoping a useful way to instrument the io stuff
>>>would already be out there.
>>>
>
>On Tue, Aug 05, 2003 at 01:23:08PM +1000, Nick Piggin wrote:
>
>>Not really.
>>For a process doing blocking reads you could measure the time
>>from when a process submits a read to when it gets the result.
>>I suppose you also need some minimum rate too but I really can't
>>see that being the problem here.
>>
>
>I'm at least aware of patches for 2.4.x that log io scheduling
>decisions in the driver, which is basically what I was hoping for.
>
>On a higher level, are you thinking there's some indication the
>io schedulers themselves aren't involved? Or that something higher-
>level should be instrumented? If so, what?
>

Yes thats what I think. Reading an mp3 shouldn't take a lot of
disk power, and seeing as its sustaining 20MB/s of writes, and
the default AS biases reads quite heavily over writes then it
would be very surprising.

Of course some minimum read _latency_ would be required: this
could actually be done easily with strace come to think of it.

Maybe some xmms mapped memory is being swapped out? But that
would be more of a VM problem.

Get the test run when the mp3 is in ram: if it can't be
reproduced then it would be worth looking into further. I guess
the process scheduler though.


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