Date: Thu, 28 Jan 1999 17:07:04 -0700 (MST) From: "Kenneth D. Merry" <ken@plutotech.com> To: pantzer@ludd.luth.se (Mattias Pantzare) Cc: freebsd-hackers@FreeBSD.ORG Subject: Re: Device statistics Message-ID: <199901290007.RAA77048@panzer.plutotech.com> In-Reply-To: <199901282019.VAA06412@zed.ludd.luth.se> from Mattias Pantzare at "Jan 28, 99 09:19:37 pm"
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Mattias Pantzare wrote... > > > What's wrong with just looking at the busy_time value that the kernel keeps > > track of? > > That is only updated when busy_count is 0, it may never get uppdated if you put > a high load on the disks (that is realy easy to do...). > > If you take samples every second and the disk get realy bussy 0.5 seconds > after the first sample you will miss half the time that the disk is in use. 0% > instead of the real value 50%. > > You will find that this is the case realy fast if you try to use busy_time. > > So, you have to look at busy_time, busy_coun, start_time and the sample time > to do anyting good of busy_time. True enough. Really, though, I'm not convinced that busy time is a very useful measurement. On any sufficiently busy disk, as you have pointed out, there will almost always be transactions outstanding. > > If you really want an accurate version of the current system uptime, you > > should probably talk to Poul-Henning about it. Providing the current > > uptime is more of a generic service, and not something that would "fit" > > into devstat.. > > Well, not realy. :-) The time that is interesting is when the sample is taken, > not when my program get a chance to get the current system uptime. But a > generic service may be good enough. I think it would be better to have a generic service, if that is what you need. Who knows, there may already be some facility to do it that I don't know about. :) Ken -- Kenneth Merry ken@plutotech.com To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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