Date: Sun, 14 Jun 2009 16:23:11 +0200 From: Attilio Rao <attilio@freebsd.org> To: Kris Kennaway <kris@freebsd.org> Cc: freebsd-smp@freebsd.org, freebsd-arch@freebsd.org Subject: Re: [PATCH] Adaptive spinning for lockmgr Message-ID: <3bbf2fe10906140723y2a99eb8an3488796ac6604134@mail.gmail.com> In-Reply-To: <4A34F4B7.5050904@FreeBSD.org> References: <3bbf2fe10906081342i6ef418e0n75e22d0b9e2543b3@mail.gmail.com> <4A34F4B7.5050904@FreeBSD.org>
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2009/6/14 Kris Kennaway <kris@freebsd.org>: > Attilio Rao wrote: >> >> This patch enables adaptive spinning for lockmgr: >> http://www.freebsd.org/~attilio/adaptive_lockmgr.diff >> >> and it should presumably improve performance on disks/vfs/buffer cache >> based benchmarks, so, if you want to try out and report any benchmarks >> result, I'd love to see it. >> Please note that there are some parameters to tune: for example, you >> would like to not enable adaptive spinning to default while you just >> want that for a class of locks (and in that case you want to apply the >> reversed logic for what is living now) or you want to use different >> values =C2=A0for retries and loops. Interested developers can refer to s= uch >> 3 variables. >> Peter Holm alredy tested that patch for about 24hours without any >> regression to report. >> >> Also note that the patch is not 100% yet as long as it needs UPDATES >> and manpages updates, but they will be added just in time before to >> commit. >> The modify is all there. > > I have a vague memory that we had tested a version of this in the past an= d > found that it caused a performance loss in common cases? =C2=A0Many lockm= gr > callers are not amenable to adaptive spinning because they have to wait o= n > slow I/O. =C2=A0Testing only with e.g. md backing might give results that= are > non-representative. I don't think I ever implemented adaptive spinning in lockmgr so if somebody else did I don't know. Said that, probabilly the best approach would be to disable it by default ad use a LK_ADAPTIVESPIN flag on a per instance basis. Such conditions, though, need to be explored a bit and I have no time to dedicate to this right now. Thanks, Attilio --=20 Peace can only be achieved by understanding - A. Einstein
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