Re: [PATCH] O11int for interactivity

Nick Piggin
2003-08-05T03:39:44Z

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.