Re: trying to understand READ_META, READ_SYNC, WRITE_SYNC & co

From: Nick Piggin
Date: Sat Jun 26 2010 - 06:10:55 EST

On Sat, Jun 26, 2010 at 11:27:59AM +0200, Christoph Hellwig wrote:
> 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.

Sorry I missed that. OK well that may be true. One would hope
it was benchmarked before being merged.

But I'm sure apps can submit fsyncs much faster than once per
few ms, like small database transactions.

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