From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Alan D. Brunelle" Date: Thu, 16 Sep 2010 11:54:05 +0000 Subject: Re: blkparse not displaying all events when tracing >1 devices? Message-Id: <4C92055D.5070201@hp.com> List-Id: References: <4C9148BF.1000306@netezza.com> In-Reply-To: <4C9148BF.1000306@netezza.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-btrace@vger.kernel.org Hm, well, the problem is (I believe) that with the "-o" option just isn't designed to work with multiple devices. Brett: The simplest thing to do for your example would be: # blktrace /dev/sdbk /dev/sdam ... # blkparse -q sdbk sdam Basically, listing each device used on the blkparse line. [That's how I (and presumably everyone else) has always done it.] The technical reason why "-o" doesn't work with multiple devices is because we use multiple threads of execution - one per device/CPU pair - and each of them opens a file named ".blktrace.". With the "-o" all of the "" values are the same - so multiple threads open the same file and try to do output. Not good. Without the "-o" we get unique files named: ".blktrace." - as the tuple (,) is unique. I suppose we could change the definition of "-o" to be: "..blktrace." - but I don't know what else this would break. So, I think what I'll do is update the documentation to just note that "-o" doesn't work with multiple devices. Regards, Alan