From owner-freebsd-hackers Sun Feb 3 19:45:12 2002 Delivered-To: freebsd-hackers@freebsd.org Received: from patrocles.silby.com (d127.as1.nwbl0.wi.voyager.net [169.207.130.193]) by hub.freebsd.org (Postfix) with ESMTP id 5395A37B405 for ; Sun, 3 Feb 2002 19:45:09 -0800 (PST) Received: from localhost (silby@localhost) by patrocles.silby.com (8.11.6/8.11.6) with ESMTP id g13LmPV13436; Sun, 3 Feb 2002 21:48:25 GMT (envelope-from silby@silby.com) X-Authentication-Warning: patrocles.silby.com: silby owned process doing -bs Date: Sun, 3 Feb 2002 21:48:25 +0000 (GMT) From: Mike Silbersack To: Luigi Rizzo Cc: Storms of Perfection , , , Subject: Re: Clock Granularity (kernel option HZ) In-Reply-To: <20020201002017.B48439@iguana.icir.org> Message-ID: <20020203214558.T13287-100000@patrocles.silby.com> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk List-ID: List-Archive: (Web Archive) List-Help: (List Instructions) List-Subscribe: List-Unsubscribe: X-Loop: FreeBSD.ORG On Fri, 1 Feb 2002, Luigi Rizzo wrote: > HZ also has an impact on select() behaviour when timeouts are > used (and device drivers using timeouts as well). > A lot of software uses select() with a very short timeout which > is usually rounded up to the next tick. If the author of the software > is unaware of what goes on (likely) there might be negative effects > on performance because such programs stay idle longer than they should. > > cheers > luigi True, I had forgotten about that effect. Ironic, since I was quite annoyed by the limitations of 10ms accuracy last semester. Increasing the resolution of select/usleep is a good argument for increasing the HZ default, but I'm not sure how great the impact would be on slower machines. Mike "Silby" Silbersack To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message