linux-kernel - Re: trying to understand READ_META, READ_SYNC, WRITE

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Date:	Wed, 23 Jun 2010 12:02:52 +0200
From:	Christoph Hellwig <hch@....de>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: trying to understand READ_META, READ_SYNC, WRITE_SYNC & co

On Mon, Jun 21, 2010 at 04:25:04PM -0400, Vivek Goyal wrote:
> In my testing in the past, this was helping if lots of sequential readers
> are running in a system (with 100ms slice each) and if there is another
> reader doing small file reads. Without meta data based preemption check,
> latency of opening small file used to be very high (Because all the sync
> sequntial reader gets to consume their 100ms slices first).
> 
> Situation should be somewhat better now after corrado's changes of
> reducing slice length dynamically. But I suspect that we will still
> experience significantly reduced latency for small file reads in presece
> of multiple sequntial reads going on.

Any chance we could create a benchmark suite for the I/O schedulers?
I'd really like to get these annotations correct, and having an
automated suite that shows the numbers for the interesting workloads
would help greatly with that.

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