Messages in this thread | | | Date | Thu, 17 Apr 2008 09:10:12 +0200 | From | Jens Axboe <> | Subject | Re: [RESEND][RFC] BFQ I/O Scheduler |
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On Thu, Apr 17 2008, Paolo Valente wrote: > Pavel Machek ha scritto: > > > >>In the first type of tests, to achieve a higher throughput than CFQ > >>(with the default 100 ms time slice), the maximum budget for BFQ > >>had to be set to at least 4k sectors. Using the same value for the > >> > > > >Hmm, 4k sectors is ~40 seconds worst case, no? That's quite long... > > > Actually, in the worst case among our tests, the aggregate throughput > with 4k sectors was ~ 20 MB/s, hence the time for 4k sectors ~ 4k * 512 > / 20M = 100 ms.
That's not worse case, it is pretty close to BEST case. Worst case is 4k of sectors, with each being a 512b IO and causing a full stroke seek. For that type of workload, even a modern sata hard drive will be doing 500kb/sec or less. That's rougly a thousand sectors per seconds, so ~4 seconds worst case for 4k sectors.
-- Jens Axboe
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