Messages in this thread | | | Date | Mon, 18 Dec 2006 23:54:21 +1100 | From | Nick Piggin <> | Subject | Re: Linux disk performance. |
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Manish Regmi wrote: > On 12/18/06, Arjan van de Ven <arjan@infradead.org> wrote: > >> if you want truely really smooth writes you'll have to work for it, >> since "bumpy" writes tend to be better for performance so naturally the >> kernel will favor those. >> >> to get smooth writes you'll need to do a threaded setup where you do an >> msync/fdatasync/sync_file_range on a frequent-but-regular interval from >> a thread. Be aware that this is quite likely to give you lower maximum >> performance than the batching behavior though. >> > > Thanks... > > But isn't O_DIRECT supposed to bypass buffering in Kernel? > Doesn't it directly write to disk? > I tried to put fdatasync() at regular intervals but there was no > visible effect. >
I don't know exactly how to interpret the numbers you gave, but they look like they might be a (HZ quantised) delay coming from block layer plugging.
O_DIRECT bypasses caching, but not (all) buffering.
Not sure whether the block layer can handle an unplug_delay set to 0, but that might be something to try (see block/ll_rw_blk.c).
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