[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <1347770892.6952.40.camel@marge.simpson.net>
Date: Sun, 16 Sep 2012 06:48:12 +0200
From: Mike Galbraith <efault@....de>
To: richard -rw- weinberger <richard.weinberger@...il.com>
Cc: Andi Kleen <andi@...stfloor.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Borislav Petkov <bp@...en8.de>,
Nikolay Ulyanitsky <lystor@...il.com>,
linux-kernel@...r.kernel.org,
Andreas Herrmann <andreas.herrmann3@....com>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...nel.org>
Subject: Re: 20% performance drop on PostgreSQL 9.2 from kernel 3.5.3 to
3.6-rc5 on AMD chipsets - bisected
On Sat, 2012-09-15 at 19:08 +0200, richard -rw- weinberger wrote:
> On Sat, Sep 15, 2012 at 6:36 PM, Mike Galbraith <efault@....de> wrote:
> >> Just using futex is unfortunately not the answer either.
> >
> > Yes, postgress performs loads better with it's spinlocks, but due to
> > that, it necessarily _hates_ preemption. How the is the scheduler
> > supposed to know that any specific userland task _really_ shouldn't be
> > preempted at any specific time, else bad things follow?
>
> Why perform custom userspace spinlocks better than futex() based ones?
> I thought we have futex() to get rid of the custom ones...
> Makes futex() only sense when things like priority inheritance are needed?
Dunno. Likely because data doesn't go cold when you spin a bit, but go
to sleep and the next guy may stomp cache flat with size XXL boots.
-Mike
--
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/
Powered by blists - more mailing lists