Date: Mon, 10 Feb 2003 01:13:17 -0800 From: David Schultz <dschultz@uclink.Berkeley.EDU> To: Poul-Henning Kamp <phk@phk.freebsd.dk> Cc: arch@FreeBSD.ORG Subject: Re: Our lemming-syncer caught in the act. Message-ID: <20030210091317.GD5165@HAL9000.homeunix.com> In-Reply-To: <31118.1044817404@critter.freebsd.dk> References: <31118.1044817404@critter.freebsd.dk>
next in thread | previous in thread | raw e-mail | index | archive | help
Thus spake Poul-Henning Kamp <phk@phk.freebsd.dk>: > I have suspected our syncer of being subobtimal for some time, based > simply on my perception of the disk-light on my laptop and the > dynamics of the "dirty" counter in systat. > > I played with the new GEOM I/O statistics stuff and guess what: I > caught it in the act: > > http://phk.freebsd.dk/misc/disk.png > > Green is the number of unfinished requests. > > Most of the red "impulse" represents one request finishing after > as many milliseconds as it is tall. The remainder of the impulses > cover more than one request, the height is then the average of the > time it has taken to service them. > > An image is worth a thousand words, but in this case it only > says three words: "Man, that sucks!". When a large file times out, a significant amount of I/O can be generated. This is still far better than the old syncer that flushed everything every 30 seconds. The reasons for this behavior are explained in src/sys/ufs/ffs/README. After reading that, do you still think it makes sense to try to do better? To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-arch" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?20030210091317.GD5165>