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    SubjectRe: [PATCH 0/8][RFC] IO latency/throughput fixes
    On Mon, Apr 06 2009, Jens Axboe wrote:
    > 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

    And here is that latter test again with NCQ disabled on the drive:

    fsync time: 0.0092s
    fsync time: 0.7815s
    fsync time: 0.6490s
    fsync time: 0.7894s
    fsync time: 0.5385s
    fsync time: 0.6598s
    fsync time: 0.7701s
    fsync time: 0.2155s
    fsync time: 0.0901s
    fsync time: 0.2765s
    fsync time: 0.2879s
    fsync time: 0.2882s
    fsync time: 0.2457s
    fsync time: 0.4319s
    fsync time: 0.3752s

    It stays nicely below 1s.

    --
    Jens Axboe



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