From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Date: Thu, 12 Apr 2007 11:29:20 +0000 Subject: Re: BLK_TA_ISSUE Message-Id: <20070412112920.GB19066@kernel.dk> List-Id: References: <1176341579.3409.2.camel@localhost.localdomain> In-Reply-To: <1176341579.3409.2.camel@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-btrace@vger.kernel.org On Wed, Apr 11 2007, Ming Zhang wrote: > Hi All > > For this ISSUE event, currently it is in elv_next_request(), any idea > why it is not in elv_dequeue_request() which is where the request marked > as on-the-fly and send to lower level? elv_next_request() is the driver hand-off point, so should be pretty close to the issue time unless the request gets requeued due to some busy condition (which will also be logged). elv_dequeue_request() may happen much later, some drivers do it right before calling the io completion handler - IDE does this - since it leaves the request on the queue list for the duration of the operation. So moving the ISSUE event to elv_dequeue_request() would not be correct. -- Jens Axboe