Re: [GIT PULL] Ext3 latency fixes

Linus Torvalds
2009-04-04T15:59:58Z

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