From: Jens Axboe <jens.axboe@oracle.com>
To: Joshua Aune <luken@omner.org>
Cc: Chris Worley <worleys@gmail.com>, fio@vger.kernel.org
Subject: Re: What's the right way to measure latency?
Date: Mon, 27 Apr 2009 08:03:57 +0200 [thread overview]
Message-ID: <20090427060356.GV4593@kernel.dk> (raw)
In-Reply-To: <530FE590-63A6-4EEE-81EF-1BE87EC6A707@omner.org>
On Sun, Apr 26 2009, Joshua Aune wrote:
>
> On Apr 26, 2009, at 7:44 AM, Chris Worley wrote:
>
>> The results show two latency numbers: clat and slat... what are these?
>
> slat is not there for the sync engines but exists for libaio, submit
> latency. clat sounds like completion latency.
It's in the HOWTO :-)
Basically slat is the time it too to enter the kernel and submit the IO
(submission latency) and clat is the time it took from submission to the
IO completed (completion latency). With the sync engines you cannot
separate the two, since when the submission syscall completes the IO has
also completed. Hence they have only clat numbers, where the async
engine has the ability to measure both.
--
Jens Axboe
prev parent reply other threads:[~2009-04-27 6:03 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-26 13:44 What's the right way to measure latency? Chris Worley
2009-04-26 13:49 ` Joshua Aune
2009-04-27 6:03 ` Jens Axboe [this message]
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