From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Alan D. Brunelle" Date: Mon, 26 Mar 2007 13:58:58 +0000 Subject: Re: how to understand the Q2Q in btt result? Message-Id: <4607D1A2.6040904@hp.com> List-Id: References: <1174876819.6887.2.camel@localhost.localdomain> In-Reply-To: <1174876819.6887.2.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-btrace@vger.kernel.org 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 >>> >>> >>> - >>> To unsubscribe from this list: send the line "unsubscribe linux-btrace" in >>> the body of a message to majordomo@vger.kernel.org >>> More majordomo info at http://vger.kernel.org/majordomo-info.html >>> >>> >> - >> To unsubscribe from this list: send the line "unsubscribe linux-btrace" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >> > > - > To unsubscribe from this list: send the line "unsubscribe linux-btrace" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >