On Fri, 2006-12-08 at 13:05 +0100, Jens Axboe wrote: > On Thu, Dec 07 2006, Avantika Mathur wrote: > > Hi Jens, > > (you probably noticed now, but the [email protected] email is no longer > valid) I saw that, thanks! > > I've noticed a performance gap between the cfq scheduler and other io > > schedulers when running the rawio benchmark. > > Results from rawio on 2.6.19, cfq and noop schedulers: > > > > CFQ: > > > > procs device num read KB/sec I/O Ops/sec > > ----- --------------- ---------- ------- -------------- > > 16 /dev/sda 16412 8338 2084 > > ----- --------------- ---------- ------- -------------- > > 16 16412 8338 2084 > > > > Total run time 0.492072 seconds > > > > > > NOOP: > > > > procs device num read KB/sec I/O Ops/sec > > ----- --------------- ---------- ------- -------------- > > 16 /dev/sda 16399 29224 7306 > > ----- --------------- ---------- ------- -------------- > > 16 16399 29224 7306 > > > > Total run time 0.140284 seconds > > > > The benchmark workload is 16 processes running 4k random reads. > > > > Is this performance gap a known issue? > > CFQ could be a little slower at this benchmark, but your results are > much worse than I would expect. What is the queueing depth of sda? How > are you invoking rawio? I am running rawio with the following options: rawread -p 16 -m 1 -d 1 -x -z -t 0 -s 4096 The queue depth on sda is 4. > > Your runtime is very low, how does it look if you allow the test to run > for much longer? 30MiB/sec random read bandwidth seems very high, I'm > wondering what exactly is being tested here. > rawio is actually performing sequential reads, but I don't believe it is purely sequential with the multiple processes. I am currently running the test with longer runtimes and will post results once it is complete. I've also attached the rawio source. Thanks, Avantika
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