Re: [PATCH 0/8][RFC] IO latency/throughput fixes

[Jens Axboe <jens.axboe@oracle.com>]

On Mon, Apr 06 2009, Jens Axboe wrote:
> Hi,
> 
> This is a set of patches that I worked on today in the hopes
> of furthering the latency goals and at least fixing some of
> the write regression with fwrite + fsync that current -git
> is suffering from.
> 
> I haven't done any latency tests yet, I'm just tossing this
> out there so we can collaborate on improving things. What I
> did test was the silly fwrite() + fsync() loop test, which
> is a LOT slower in current -git that it used to be. The test
> is basically:
> 
> 	while (nr--) {
> 		f = fopen();
> 		fprintf(f, "Some data here\n");
> 		fsync(fileno(f));
> 		fclose(f);
> 	}
> 
> which (for nr == 2000) takes 16 seconds in -git, completes
> in 0.9s with the patches.

Ran the fsync-tester [1]. Drive is a 3-4 years old SATA drive, fs is
ext3/writeback. IO scheduler is CFQ.

fsync time: 0.0402s
fsync time: 0.6572s
fsync time: 0.3187s
fsync time: 0.2901s
fsync time: 0.1478s
fsync time: 0.4158s
fsync time: 0.2815s
fsync time: 0.3216s
fsync time: 0.1604s
fsync time: 0.1929s
fsync time: 0.2413s
fsync time: 0.2138s
fsync time: 0.2441s
fsync time: 0.2785s
fsync time: 0.2640s

And with Linus torture dd running in the background:

fsync time: 0.0109s
fsync time: 0.5236s
fsync time: 1.2108s
fsync time: 0.2999s
fsync time: 1.5286s
fsync time: 0.2549s
fsync time: 0.4164s
fsync time: 1.1586s
fsync time: 1.6630s
fsync time: 0.6949s
fsync time: 1.0102s
fsync time: 0.3715s
fsync time: 0.6553s

[1]
http://www.gossamer-threads.com/lists/engine?do=post_attachment;postatt_id=33847;list=linux

-- 
Jens Axboe