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Gmane
From: Linus Torvalds <torvalds <at> linux-foundation.org>
Subject: Re: [GIT PULL] Ext3 latency fixes
Newsgroups: gmane.comp.file-systems.ext4
Date: Saturday 4th April 2009 15:57:28 UTC (over 8 years ago)
On Sat, 4 Apr 2009, Jens Axboe wrote:
> 
> Big nack on this patch. Ted, this is EXACTLY where I told you we saw big
> write regressions (sqlite performance drops by a factor of 4-5). Do a
> git log on fs/buffer.c and see the original patch (which does what your
> patch does) and the later revert. No idea why you are now suggestion
> making that exact change?!

Jens, if I can re-create the 'fsync' times (I haven't yet), then the 
default scheduler _will_ be switched to AS.

> Low latency is nice, but not at the cost of 4-5x throughput for real
> world cases.

I'm sorry, but that fsync thing _is_ a real-world case, and it's the one 
that a hell of a lot more people care about than some idiotic sqlite 
throughput issue.

You have a test-case now. Consider it a priority, or consider CFQ to be a 
"for crazy servers that only care about throughput".

Quite frankly, the fact that I can see _seconds_ of latencies with a 
really good SSD is not acceptable. The fact that it is by design is even 
less so.

Latency is more important than throughput. It's that simple.

			Linus
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