Date: Wed, 17 Jul 2013 23:59:10 +0100 From: "Steven Hartland" <smh@freebsd.org> To: "John Baldwin" <jhb@freebsd.org>, <freebsd-stable@freebsd.org> Cc: Konstantin Belousov <kostikbel@gmail.com>, Mark Johnston <markj@freebsd.org> Subject: Re: syncer causing latency spikes Message-ID: <DD96FF6123B14D61B9CE1C42572D517A@multiplay.co.uk> References: <20130717180720.GA8289@charmander> <20130717191852.GS5991@kib.kiev.ua> <201307171615.35484.jhb@freebsd.org>
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----- Original Message ----- From: "John Baldwin" <jhb@freebsd.org> > On Wednesday, July 17, 2013 3:18:52 pm Konstantin Belousov wrote: >> On Wed, Jul 17, 2013 at 02:07:55PM -0400, Mark Johnston wrote: >> > During such an fsync, DTrace shows me that syncer sleeps of 50-200ms are >> > happening up to 8 or 10 times a second. When this happens, a bunch of >> > postgres threads become blocked in vn_write() waiting for the vnode lock >> > to become free. It looks like the write-clustering code is limited to >> > using (nswbuf / 2) pbufs, and FreeBSD prevents one from setting nswbuf >> > to anything greater than 256. >> Syncer is probably just a victim of profiling. Would postgres called >> fsync(2), you then blame the fsync code for the pauses. >> >> Just add a tunable to allow the user to manually-tune the nswbuf, >> regardless of the buffer cache sizing. And yes, nswbuf default max >> probably should be bumped to something like 1024, at least on 64bit >> architectures which do not starve for kernel memory. > > Also, if you are seeing I/O stalls with mfi(4), then you might need a > firmware update for your mfi(4) controller. cc'ing smh@ who knows more about > that particular issue (IIRC). Indeed if your seeing any IO timeouts in /var/log/messages or the console there is a know issue in older mfi(4) firmware which can cause extended IO stalls. We believe that fixed firmware packages include "APP" version > *.130.* For Dell branded HW that corrisponds with FW package version 21.2.1-0000 Regards Steve
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