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From: Matthew Kirkwood <matthew@hairy.beasts.org>
To: Jonathan Lahr <lahr@sequent.com>
Cc: Anton Blanchard <anton@linuxcare.com.au>, linux-kernel@vger.kernel.org
Subject: Re: kernel lock contention and scalability
Date: Tue, 6 Mar 2001 23:39:17 +0000 (GMT)	[thread overview]
Message-ID: <Pine.LNX.4.10.10103062318190.26554-100000@sphinx.mythic-beasts.com> (raw)
In-Reply-To: <20010306144552.G6451@w-lahr.des.sequent.com>

On Tue, 6 Mar 2001, Jonathan Lahr wrote:

[ sorry to reply over another reply, but I don't have
  the original of this ]

> > Tridge and I tried out the postgresql benchmark you used here and this
> > contention is due to a bug in postgres. From a quick strace, we found
> > the threads do a load of select(0, NULL, NULL, NULL, {0,0}).

I can shed some light on this (though I'm far from a PG hacker).

Postgres can use either of two locking methods -- SysV semaphores
(which it tries to avoid, asusming that they'll be too heavy) or
userspace spinlocks (via inline assembler on platforms which support
it).

In the slow path of a spinlock_acquire they busy wait for a few
cycles, and then call schedule with a zero timeout assuming that
it'll basically do the same as a sched_yield() but more portably.

Matthew.


  reply	other threads:[~2001-03-06 23:40 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2001-02-15 18:46 kernel lock contention and scalability Jonathan Lahr
2001-02-25  9:52 ` Manfred Spraul
2001-03-05 18:41   ` Jonathan Lahr
2001-03-05  0:38 ` Anton Blanchard
2001-03-06 22:45   ` Jonathan Lahr
2001-03-06 23:39     ` Matthew Kirkwood [this message]
2001-03-07  0:28       ` Tim Wright
2001-03-07  3:12         ` Jeff Dike
2001-03-07 22:13           ` Tim Wright
2001-03-08 23:26             ` Jeff Dike
2001-03-11  6:50       ` Anton Blanchard
2001-03-11  6:26     ` Anton Blanchard
     [not found] <98454d$19p9h$1@fido.engr.sgi.com>
2001-03-07  2:55 ` Rajagopal Ananthanarayanan
2001-03-07  5:48   ` Jeff Dike

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