Date: Thu, 14 Sep 2006 13:35:57 -0400 From: Kris Kennaway <kris@obsecurity.org> To: Gary Corcoran <gcorcoran@rcn.com> Cc: Dag-Erling Sm?rgrav <des@des.no>, freebsd-hackers@freebsd.org Subject: Re: numbers don't lie ... Message-ID: <20060914173556.GA55017@xor.obsecurity.org> In-Reply-To: <45099123.4000500@rcn.com> References: <E1GNOLq-000DC2-1Q@cs1.cs.huji.ac.il> <863bauk3gp.fsf@dwp.des.no> <45099123.4000500@rcn.com>
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--17pEHd4RhPHOinZp Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Thu, Sep 14, 2006 at 01:28:03PM -0400, Gary Corcoran wrote: > The confusing thing is that I thought 'real' time should be >=3D 'user' += =20 > 'sys'. No. This is at best only ever approximately true on a uniprocessor machine when there is no blocking I/O being performed. A bit of thought about the nature of a multiprocessor system will lead you to the conclusion that when two processes are executing in parallel, the real time will be less than the sum of both user and system times - that's what it means to have parallelism. > But here 'user' is much greater than 'real' for both machines! The sense= I > got from the other messages in this thread is that 'user' time is somewhat > meaningless (i.e. unreliable as a measure) in a multi-CPU and/or=20 > hyperthreading > environment. Can you clarify? See my earlier messages; it's only meaningless if you don't understand its meaning. Kris --17pEHd4RhPHOinZp Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (FreeBSD) iD8DBQFFCZL8Wry0BWjoQKURAivZAKC2U5P+PcRd9Df7fKuKpzQ14NJEsgCgkiqO pjKy1btFtCfLTDi2fq9CYV8= =mzcU -----END PGP SIGNATURE----- --17pEHd4RhPHOinZp--
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