Messages in this thread | | | Subject | Re: [PATCH][2.6-mm] Readahead issues and AIO read speedup | From | Ram Pai <> | Date | 22 Sep 2003 17:41:07 -0700 |
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On Thu, 2003-08-07 at 13:58, Andrew Morton wrote: > Badari Pulavarty <pbadari@us.ibm.com> wrote: > > > > On Thursday 07 August 2003 10:39 am, Andrew Morton wrote: > > > Badari Pulavarty <pbadari@us.ibm.com> wrote: > > > > We should do readahead of actual pages required by the current > > > > read would be correct solution. (like Suparna suggested). > > > > > > I repeat: what will be the effect of this if all those pages are already in > > > pagecache? > > > > Hmm !! Do you think just peeking at pagecache and bailing out if > > nothing needed to be done, is too expensive ? Anyway, slow read > > code has to do this later. Doing it in readahead one more time causes > > significant perf. hit ? > > It has been observed, yes.
we found substantial improvements (around 20% )in Database decision support work load on Filesystems.
To address your concern regarding possible SDET regression generated by this patch, we (Steve Pratt) ran a bunch of regression tests on 2.6.0test5-mm2(with and without the patch). I have pasted the results of SDET and Kernel Bench. We did not find any noticable performance regression.
Here are some results from Steve on test5-mm2 **************************************************************************
sdet comparison of 2.6.0-test5-mm2 vs 2.6.0-test5mm2-without-READAHEAD-patch
Results:Throughput
tolerance = 0.00 + 3.00% of 2.6.0-test5-mm2 2.6.0-test5-mm2 2.6.0-test5mm2-without-READAHEAD Threads Ops/sec Ops/sec %diff diff tolerance ---------- ------------ ------------ -------- ------------ ------------ 1 3089 3103 0.45 14.00 92.67 4 11181 11294 1.01 113.00 335.43 16 18436 18530 0.51 94.00 553.08 64 18867 19002 0.72 135.00 566.01
**************************************************************************** ************************************************************************** kernbench comparison of 2.6.0-test5-mm2 vs 2.6.0-test5mm2-without-READAHEAD
Results:Elapsed Time tolerance = 0.00 + 3.00% of 2.6.0-test5-mm2 2.6.0-test5-mm2 2.6.0-test5mm2-without-READAHEAD Seconds Seconds %diff diff tolerance ---------- ------------ ------------ -------- ------------ ------------ 2 96.015 95.035 -1.02 -0.98 2.88
**************************************************************************
Would you like us to run some other tests?
Thanks, RP
> > > And also, do you think this is the most common case ? > > It is a very common case. It's one we need to care for. Especially when > lots of CPUs are hitting the same file. > > There are things we can do to tweak it up, such as adding a max_index to > find_get_pages(), then do multipage lookups, etc. But not doing it at all > is always the fastest way. > - > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >
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