Date: Mon, 01 Apr 2002 14:28:31 +0200 From: Poul-Henning Kamp <phk@critter.freebsd.dk> To: Dag-Erling Smorgrav <des@ofug.org> Cc: arch@FreeBSD.ORG Subject: Re: mutex profiling Message-ID: <4905.1017664111@critter.freebsd.dk> In-Reply-To: Your message of "01 Apr 2002 13:38:01 %2B0200." <xzp4rivejja.fsf@flood.ping.uio.no>
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In message <xzp4rivejja.fsf@flood.ping.uio.no>, Dag-Erling Smorgrav writes:
>Poul-Henning Kamp <phk@critter.freebsd.dk> writes:
>> With the footnote that the TSC's are not synchronized on SMP
>> systems [...]
>
>We tried using {,get}nanouptime() instead, but got nothing but
>zeroes...
nanouptime() should not get you zeros, but it would be slower than
TSC. getnanouptime would hopefully give you all zeros.
I didn't mean to imply that the TSC was wrong as such, but merely
wanted to point to the fact that a mutex locked on one CPU and
unlocked on another will (likely) screw up your numbers big time.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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