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Date: Tue, 14 Oct 2008 00:19:11 +0200 From: kenneth johansson <ken@...jo.org> To: Grant Grundler <grundler@...gle.com> Cc: linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: weird throughput on write to SATA disk On Mon, 2008-10-13 at 14:34 -0700, Grant Grundler wrote: > On Mon, Oct 13, 2008 at 2:22 PM, kenneth johansson <ken@...jo.org> wrote: > > On Mon, 2008-10-13 at 14:07 -0700, Grant Grundler wrote: > >> On Mon, Oct 13, 2008 at 12:19 PM, kenneth johansson <ken@...jo.org> wrote: > >> > When writing data to /dev/sdb (that is the whole disk and no filesystem) > >> > it starts out ok around 100MB/sec but soon end up doing considerably > >> > worse. For prolonged times lasting several minutes it hovers in the > >> > 20-30MB/sec. > >> > >> Is the application using "O_DIRECT"? > > > > no just open then write no fancy stuff > > > >> If not, could be issue with how VM writeback is (not) working. > > > > the access pattern is the simplest possible. Is there any knobs I could > > try to adjust. > > > >> Can you reproduce this using fio or even "dd"? > >> (See git://git.kernel.dk/fio) > > > > dd is having the same effect. > > Can you try "dd oflag=direct if=/dev/null of=/dev/sdb bs=64k"? I changed to use O_DIRECT and it's much more consistent now. 69-75 with 74 about 95% of the time. the disk is supposed to have 105 115 sustained data rate. -- 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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