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    SubjectRe: RFC on io-stalls patch
    On Mon, Jul 14 2003, Chris Mason wrote:
    > On Mon, 2003-07-14 at 18:45, Andrea Arcangeli wrote:
    > > On Mon, Jul 14, 2003 at 04:34:41PM -0400, Chris Mason wrote:
    > > > patch. It's a good starting point for the question "can we do better
    > > > for reads?" (clearly the answer is yes).
    > >
    > > Jens's patch will block every writers until the parallel sync readers go
    > > away. if we add a 5 seconds delay for every write, sure readers will
    > > run faster too in contest, and in turn it's not obvious to me it's
    > > necessairly a good starting point.
    > For real server workloads I agree the patch isn't a good idea. But
    > Jens' workload had a small number of kernel compilers (was it one proc
    > or make -j4 or so?), so clearly the writers could still make progress.
    > This doesn't mean I want the patch but it does mean the numbers are
    > worth thinking about ;-)
    > If we go back to Jens' numbers:
    > ctar_load:
    > Kernel [runs] Time CPU% Loads LCPU% Ratio
    > 2.4.22-pre5 3 235 114.0 25.0 22.1 1.75
    > 2.4.22-pre5-axboe 3 194 138.1 19.7 20.6 1.46
    > ^^^^^^
    > The loads column is the number of times ctar_load managed to run during
    > the kernel compile, and the patched kernel loses each time. This must
    > partially be caused by the lower run time overall, but it is still
    > important data. It would be better if contest gave us some kind of
    > throughput numbers (avg load time or something).

    Well, look at the ratio given the run times listed. You'll see that they
    are extremely close (0.1064 for 2.4.22-pre5 vs 0.1015 for

    It just shows that we are not hitting the possible bad problems in these
    work loads.

    Jens Axboe

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