On Wed, Feb 03, 2010 at 02:27:56PM +0800, Wu Fengguang wrote: > Vivek, > > On Wed, Feb 03, 2010 at 06:38:03AM +0800, Vivek Goyal wrote: > > On Tue, Feb 02, 2010 at 11:28:35PM +0800, Wu Fengguang wrote: > > > Andrew, > > > > > > This is to lift default readahead size to 512KB, which I believe yields > > > more I/O throughput without noticeably increasing I/O latency for today's HDD. > > > > > > > Hi Fengguang, > > > > I was doing a quick test with the patches. I was using fio to run some > > sequential reader threads. I have got one access to one Lun from an HP > > EVA. In my case it looks like with the patches throughput has come down. > > Thank you for the quick testing! > > This patchset does 3 things: > > 1) 512K readahead size > 2) new readahead algorithms > 3) new readahead tracing/stats interfaces > > (1) will impact performance, while (2) _might_ impact performance in > case of bugs. > > Would you kindly retest the patchset with readahead size manually set > to 128KB? That would help identify the root cause of the performance > drop: > > DEV=sda > echo 128 > /sys/block/$DEV/queue/read_ahead_kb > I have got two paths to the HP EVA and got multipath device setup(dm-3). I noticed with vanilla kernel read_ahead_kb=128 after boot but with your patches applied it is set to 4. So looks like something went wrong with device size/capacity detection hence wrong defaults. Manually setting read_ahead_kb=512, got me better performance as compare to vanilla kernel. AVERAGE[bsr] ------- job Set NR ReadBW(KB/s) MaxClat(us) WriteBW(KB/s) MaxClat(us) --- --- -- ------------ ----------- ------------- ----------- bsr 3 1 190302 97937.3 0 0 bsr 3 2 185636 223286 0 0 bsr 3 4 185986 363658 0 0 bsr 3 8 184352 428478 0 0 bsr 3 16 185646 594311 0 0 Thanks Vivek > The readahead stats provided by the patchset are very useful for > analyzing the problem: > > mount -t debugfs none /debug > > # for each benchmark: > echo > /debug/readahead/stats # reset counters > # do benchmark > cat /debug/readahead/stats # check counters > > Thanks, > Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
