On Sat, Nov 01, 2008 at 04:29:18AM -0400, Justin Piszcz wrote: > Overall the raw speed according to vmstat seems to increase as you add more > load to the server. So I decided to time running three jobs on two parts > of data and compare it with a single job that proceses them all. > > Three jobs run con-currently: (2 parts/each): > > 1- 59.99user 18.25system 2:02.07elapsed 64%CPU (0avgtext+0avgdata 0maxresident)k > 0inputs+0outputs (0major+21000minor)pagefaults 0swaps > > 2- 59.86user 17.78system 1:59.96elapsed 64%CPU (0avgtext+0avgdata 0maxresident)k > 0inputs+0outputs (21major+20958minor)pagefaults 0swaps > > 3- 74.77user 22.83system 2:13.30elapsed 73%CPU (0avgtext+0avgdata 0maxresident)k > 0inputs+0outputs (36major+21827minor)pagefaults 0swaps > > One job with (6 parts): > > 1 188.66user 56.84system 4:38.52elapsed 88%CPU (0avgtext+0avgdata 0maxresident)k > 0inputs+0outputs (71major+43245minor)pagefaults 0swaps > > Why is running 3 jobs con-currently that take care of two parts each more than > twice as fast than running one job for six parts? Usually this is because the workload is I/O latency sensitive and so can't keep the disk fully busy because it is serialising on I/O. By running jobs concurrently you are reducing the impact of serialising on an I/O because there are still two other concurrent jobs issuing I/O instead of none... > I am using XFS and md/RAID-5, the CFQ scheduler and kernel 2.6.27.4. > Is this more of an md/raid issue ( I am guessing ) than XFS? I remember > reading of some RAID acceleration patches awhile back that were supposed > to boost performance quite a bit, what happened to them? Without further information, I'd say a pure application issue - the disk subsystem is clearly fast enough to handle much higher load than the single job is capable of issuing. Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
