Date: Sun, 2 Oct 2005 10:47:18 +0930 From: Greg 'groggy' Lehey <grog@FreeBSD.org> To: Kris Kennaway <kris@obsecurity.org> Cc: Ansar Mohammed <ansarm@gmail.com>, freebsd-questions@freebsd.org Subject: "BGL", Giant and kernel lockups Message-ID: <20051002011718.GE95042@wantadilla.lemis.com> In-Reply-To: <20051001081124.GA63863@xor.obsecurity.org> References: <20050930204601.GA31598@xor.obsecurity.org> <000901c5c63c$5c2fa190$0b02a8c0@northamerica.corp.microsoft.com> <20051001081124.GA63863@xor.obsecurity.org>
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--orO6xySwJI16pVnm Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Saturday, 1 October 2005 at 4:11:25 -0400, Kris Kennaway wrote: > On Fri, Sep 30, 2005 at 11:58:14PM -0400, Ansar Mohammed wrote: >> I love FreeBSD. I have been using it since 2.x. I have never had any >> problems with it. Rock Solid. Never a single kernel panic. >> >> Then I come across this article in a comparison between Linux and >> FreeBSD saying that FreeBSD has kernel locking >> issues. Specifically, a problem nicknamed BGL or Big Giant Lock. It >> seems that it affects SMP systems under high load. > > Sounds like a pretty simplistic summary, but as I mentioned it's out > of date anyway. I don't think that answers his question. I think that most people (with the exception of Erik Trulsson) have missed the fact that Ansar has a misconception about the meaning of "BGL". This is not a "problem", and it has nothing to do with kernel stability (lockups); it has to do with the way the kernel protects its data integrity in normal operation. All kernels perform locking for this purpose. Older UNIX (including BSD) and Linux systems used a thing called the "Big Kernel Lock" or Giant to ensure that only one process, system wide, had access to the entire kernel at a time. This was a performance issue, not a stability issue. All modern systems have relaxed this requirement. You may like to look at my (now somewhat out of date) papers on FreeBSD SMPNg, available at http://www.lemis.com/grog/Papers/. There should be more up-to-date information on the current state of the FreeBSD implementation. Greg -- When replying to this message, please copy the original recipients. If you don't, I may ignore the reply or reply to the original recipients. For more information, see http://www.lemis.com/questions.html See complete headers for address and phone numbers. --orO6xySwJI16pVnm Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (FreeBSD) iD8DBQFDPzUeIubykFB6QiMRAlsKAJ9ugrzC7Jyuqxx+3HnAS8ZMXyCTxwCfbk7+ aXCEnmUm+T6zr64BzL5bvzQ= =O0S1 -----END PGP SIGNATURE----- --orO6xySwJI16pVnm--
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