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

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Message-ID: <20100626092759.GA25896@lst.de>
Date:	Sat, 26 Jun 2010 11:27:59 +0200
From:	Christoph Hellwig <hch@....de>
To:	Nick Piggin <npiggin@...e.de>
Cc:	Christoph Hellwig <hch@....de>, Vivek Goyal <vgoyal@...hat.com>,
	Jens Axboe <axboe@...nel.dk>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: trying to understand READ_META, READ_SYNC, WRITE_SYNC & co

On Sat, Jun 26, 2010 at 07:25:56PM +1000, Nick Piggin wrote:
> Biggest thing is multiple small files operations like on the same
> directory. Best case I measured back when doing AS io scheduler
> versus deadline was about 100x improvement on a uncached kernel
> grep workload when competing with a streaming writeout (the writeout
> probably ended up going somewhat slower naturally, but it is fairer).

As I mentioned below I absolutely see the case for reads.  A normal
grep basically is a dependent read kind of workload.  For for writes
it should either be O_SYNC-style workloads or batched I/O. 
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