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From: Pavel Machek <pavel@suse.cz>
To: "Richard B. Johnson" <root@chaos.analogic.com>
Cc: Roger Larsson <roger.larsson@norran.net>,
	Linux kernel <linux-kernel@vger.kernel.org>
Subject: Re: SMP spin-locks
Date: Fri, 15 Jun 2001 15:52:52 +0000	[thread overview]
Message-ID: <20010615155251.C37@toy.ucw.cz> (raw)
In-Reply-To: <200106142045.f5EKjLI14289@mailf.telia.com> <Pine.LNX.3.95.1010614165153.16430A-100000@chaos.analogic.com>
In-Reply-To: <Pine.LNX.3.95.1010614165153.16430A-100000@chaos.analogic.com>; from root@chaos.analogic.com on Thu, Jun 14, 2001 at 05:05:07PM -0400

Hi!

> The 'read()' routine uses a spinlock when it modifies pointers.
> 
> I started to look into where all the CPU clocks were going. The
> SMP spinlock code is where it's going. There is often contention
> for the lock because interrupts normally occur at 50 to 60 kHz.
> 
> When there is contention, a very long........jump occurs into
> the test.lock segment. I think this is flushing queues. 

On UP, there's *never* contention on the lock, because irqsave lock
disables interrupts. Right? Something else must be slowing you.

								Pavel
PS: But that's bad. Performance should not come down twice --
this will bite you even on real SMP.

-- 
Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt,
details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.


      parent reply	other threads:[~2001-06-16 10:11 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2001-06-14 17:26 Richard B. Johnson
2001-06-14 17:32 ` David S. Miller
2001-06-14 17:35 ` Kurt Garloff
2001-06-15  6:51   ` Doug Ledford
2001-06-14 20:42 ` Roger Larsson
2001-06-14 21:05   ` Richard B. Johnson
2001-06-14 21:30     ` Roger Larsson
2001-06-15  3:21       ` Richard B. Johnson
2001-06-15  2:33         ` David Lang
2001-06-15 10:35         ` David Schwartz
2001-06-15 13:26           ` Richard B. Johnson
2001-06-15 12:10     ` Ingo Oeser
2001-06-15 12:49       ` Richard B. Johnson
2001-06-15 15:52     ` Pavel Machek [this message]

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