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Date: Wed, 19 Aug 2009 21:08:05 +0200 From: Jens Axboe <jens.axboe@...cle.com> To: Jeff Garzik <jeff@...zik.org> Cc: Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org, Eric.Moore@....com Subject: Re: [PATCH 1/3] block: add blk-iopoll, a NAPI like approach for block devices On Fri, Aug 07 2009, Jens Axboe wrote: > On Fri, Aug 07 2009, Jens Axboe wrote: > > On Fri, Aug 07 2009, Jens Axboe wrote: > > > > I'm not NAK'ing... just inserting some relevant NAPI field experience, > > > > and hoping for some numbers that better measure the costs/benefits. > > > > > > Appreciate you looking over this, and I'll certainly be posting some > > > more numbers on this. It'll largely depend on both storage, controller, > > > and worload. > > > > Here's a quick set of numbers, beating with random reads on a drive. > > Average of three runs for each, stddev is very low so confidence in the > > numbers should be high. > > > > With iopoll=0 (disabled), stock: > > > > blocksize IOPS ints/sec usr sys > > ------------------------------------------------------ > > 4k 48401 ~30500 3.36% 27.26% > > > > clat (usec): min=1052, max=21615, avg=10541.48, stdev=243.48 > > clat (usec): min=1066, max=22040, avg=10543.69, stdev=242.05 > > clat (usec): min=1057, max=23237, avg=10529.04, stdev=239.30 > > > > > > With iopoll=1 > > > > blocksize IOPS ints/sec usr sys > > ------------------------------------------------------ > > 4k 48452 ~29000 3.37% 26.47% > > > > > > clat (usec): min=1178, max=21662, avg=10542.72, stdev=247.87 > > clat (usec): min=1074, max=21783, avg=10534.14, stdev=240.54 > > clat (usec): min=1102, max=22123, avg=10509.42, stdev=225.73 > > Lets raise the bar a bit, this time using 8k reads on the faster box. > > iopoll=0 > > blocksize IOPS ints/sec usr sys > ------------------------------------------------------ > 8k 64050 ~76000 4.12% 45.01% > > clat (usec): min=1326, max=18994, avg=7967.54, stdev=214.12 > clat (usec): min=1325, max=25404, avg=7968.06, stdev=239.87 > clat (usec): min=1273, max=21414, avg=7963.43, stdev=231.27 > > > iopoll=1 > > blocksize IOPS ints/sec usr sys > ------------------------------------------------------ > 8k 64162 ~55000 4.07% 42.32% > > clat (usec): min=1380, max=19681, avg=7960.31, stdev=197.41 > clat (usec): min=1370, max=37508, avg=7954.61, stdev=210.35 > clat (usec): min=1332, max=23383, avg=7947.99, stdev=209.60 > > Again, purely a synthetic IO benchmark, but the sys reduction is > interesting. Upping the ante a bit more, this time on a really fast box. Just to show that iopoll works well even on just about the fastest CPU you can throw at it. iopoll=0 blocksize IOPS ints/sec usr sys ------------------------------------------------------ 8k 64823 ~67000 4.75% 13.41% clat (usec): min=1430, max=15770, avg=7880.60, stdev=118.95 clat (usec): min=1249, max=17810, avg=7887.34, stdev=120.39 clat (usec): min=1729, max=15473, avg=7888.13, stdev=118.70 iopoll=1 blocksize IOPS ints/sec usr sys ------------------------------------------------------ 8k 64825 ~65000 4.37% 11.39% clat (usec): min=1530, max=15195, avg=7910.01, stdev=111.43 clat (usec): min=1495, max=16180, avg=7885.11, stdev=115.56 clat (usec): min=1446, max=19733, avg=7890.46, stdev=139.05 -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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