From: "Alan D. Brunelle" <alan.brunelle@hp.com>
To: linux-btrace@vger.kernel.org
Subject: Re: how to understand the Q2Q in btt result?
Date: Mon, 26 Mar 2007 13:58:58 +0000 [thread overview]
Message-ID: <4607D1A2.6040904@hp.com> (raw)
In-Reply-To: <1174876819.6887.2.camel@localhost.localdomain>
Ming Zhang wrote:
> On Sun, 2007-03-25 at 23:51 -0400, Alan D. Brunelle wrote:
>
>> Ming Zhang wrote:
>>
>>> from btt user guide
>>>
>>> "Q2Q which measures the time between queue traces in the system.
>>> This provides some idea as to how quickly IOs are being handed to
>>> the block IO layer."
>>>
>>> does this mean the time between queuing N request and N
>>> +1 request?
>>>
>>>
>> Hi Ming -
>>
>> This is the average time between the Q traces being logged. We take the
>> difference between each succeeding Q trace, and divide the sum by the total.
>>
>
> so like block layer idle indicator.
Not quite - the block layer %util value indicates how much the
underlying device (driver) has active commands. Q2Q is more of a measure
of upper-level activity - application & file system & VM (page cache).
It indicates how quickly commands are being submitted to the block IO layer.
> maybe a similar D2D will be a nice
> device indicator as well.
>
This would be an indicator of how quickly lower-layer device drivers are
getting issued IOs. It would be trivial to implement, if you are
interested in it, I can do it...
Alan
>
>
>> Alan
>>
>>> thanks!
>>>
>>> Ming
>>>
>>>
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next prev parent reply other threads:[~2007-03-26 13:58 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-26 2:40 how to understand the Q2Q in btt result? Ming Zhang
2007-03-26 3:51 ` Alan D. Brunelle
2007-03-26 13:30 ` Ming Zhang
2007-03-26 13:58 ` Alan D. Brunelle [this message]
2007-03-26 15:00 ` Ming Zhang
2007-03-26 15:09 ` Alan D. Brunelle
2007-03-26 15:21 ` Ming Zhang
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