From owner-freebsd-hackers Wed Nov 15 11: 7:43 2000 Delivered-To: freebsd-hackers@freebsd.org Received: from brutus.conectiva.com.br (brutus.conectiva.com.br [200.250.58.146]) by hub.freebsd.org (Postfix) with ESMTP id 7FBF237B479 for ; Wed, 15 Nov 2000 11:07:39 -0800 (PST) Received: from localhost (riel@localhost) by brutus.conectiva.com.br (8.11.1/8.11.1) with ESMTP id eAFJ72c08856; Wed, 15 Nov 2000 17:07:02 -0200 X-Authentication-Warning: duckman.distro.conectiva: riel owned process doing -bs Date: Wed, 15 Nov 2000 17:07:02 -0200 (BRDT) From: Rik van Riel X-Sender: riel@duckman.distro.conectiva To: Terry Lambert Cc: void , hackers@FreeBSD.ORG Subject: Re: "iowait" CPU state In-Reply-To: <200011151730.KAA12666@usr01.primenet.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-freebsd-hackers@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG On Wed, 15 Nov 2000, Terry Lambert wrote: > > > > Thank you! This gets the me disk %busy, which is one of the things I > > > > was looking for. Now, can anyone tell me how to tell what percentage of > > > > processor time is being spent waiting for disk I/O to complete? > > > > > > Uh, none? > > > > > > If there is disk I/O pending, the processor just runs a > > > different process... am I missing your question? > > > > I guess it might be useful to see the difference between > > "true" idle time and time the system couldn't do anything > > useful because it was blocked on the disk (but /should/ > > have done something useful...). > > You mean because the programmer didn't interleave their I/O, > and wrote to a threads interface, or some other interface > that's prone to subsystem stalling, instead? Interleaving IO only makes sense when you have tons of parallelisable jobs. If you have one big serial job this doesn't buy you anything... Yes, you can use a separate thread to queue IO in advance, but in this case it might just be useful to have the %iowait statistic so you know how much work to queue in advance. Then again, this may be a bad example. I can't quite put my finger on it, but somehow I have the idea that the %iowait may be a useful statistic to keep... > Modern bloat-ware really pisses me off; I built the bind > library the other day: the frigging thing was 4M, unstripped. How does this affect the (non?-)usefullness of the %iowait statistic? regards, Rik -- "What you're running that piece of shit Gnome?!?!" -- Miguel de Icaza, UKUUG 2000 http://www.conectiva.com/ http://www.surriel.com/ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message