Messages in this thread | | | Date | Thu, 17 Apr 2008 10:48:16 +0200 | From | Pavel Machek <> | 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.
One seek is still 10msec on modern drive, right? So 4k seeks = 40seconds, no? 4seconds would correspond to 1msec per seek, which seems low.
writes with O_SYNC could force full seek on each request, right? Pavel -- (english) http://www.livejournal.com/~pavelmachek (cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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