Date: Wed, 5 Feb 2003 11:52:14 +1030 From: Greg 'groggy' Lehey <grog@FreeBSD.org> To: phk@freebsd.org Cc: Brad Knowles <brad.knowles@skynet.be>, current@freebsd.org Subject: Re: Preview: GEOMs statistics code. Message-ID: <20030205012214.GG12525@wantadilla.lemis.com> In-Reply-To: <27759.1044403667@critter.freebsd.dk> References: <a05200f08ba65f714a4e9@[146.106.12.76]> <27759.1044403667@critter.freebsd.dk>
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On Wednesday, 5 February 2003 at 1:07:47 +0100, Poul-Henning Kamp wrote:
> In message <a05200f08ba65f714a4e9@[146.106.12.76]>, Brad Knowles writes:
>> At 10:44 PM +0100 2003/02/04, Poul-Henning Kamp wrote:
>>
>>> In difference from the devstat framework which measures how big a
>>> percentage of the time a drive has one or more outstanding requests,
>>> I think that measuring the responstime is a much more useful metric.
>>> (comments, input, references welcome)
>>
>> This is queue depth versus latency, right? I don't suppose a
>> request to provide both would hold any weight with you, would it?
>
> I'm 100% wide open to suggestions. Anything I can trivally account
> for is fair game.
It looks like there are at least three statistics of interest:
1. Response time.
2. %busy. I personally think this is the most important one, but as
you say, there's no reason not to do the others as well.
3. Average number of requests waiting.
> I don't have a queue-depth as such, but I have number of
> transactions in transit. Will a snapshot of that at the time of the
> read do what you want ?
What's the difference? I would have thought that's the same thing.
> I won't be locking the stats counters, so reads may get inconsistent
> results.
This looks like a correct decision to me. I can't see any
disadvantage in slightly incorrect values, as long as they don't
accumulate.
Greg
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