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Andrew Morton wrote: > Nick Piggin <nickpiggin@yahoo.com.au> wrote: > >>Pedro Larroy wrote: >> >>>Hi >>> >>>I've been trying CFQ ioscheduler in my software raid5 with nice results, >>>I've observed that a latency pattern still exists, just as in the >>>anticipatory ioscheduler, but those spikes are now much lower (from >>>6ms with AS to 2ms with CFQ as seen in the bottom of >>>http://pedro.larroy.com/devel/iolat/analisys/), >>>plus apps seems to get a fair amount of io so they don't get starved. >>> >>>Seems a good choice for io loaded boxes. Thanks Jens Axboe. >>> >> >>Although AS isn't at its best when behind raid devices (it should >>probably be in front of them), you could be seeing some problem >>with the raid code. >> >>I'd be interested to see what the graph looks like with elevator=noop > > > This isn't a very surprising result, is it? AS throws away latency to gain > throughput. Pedro is measuring latency... > Well I think Pedro actually means *seconds*, not ms. The URL shows AS peaks at nearly 10 seconds latency, and CFQ over 2s. It really seems like a raid problem though, because latency measured at the individual devices is under 250ms for AS. - 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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