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On Fri, Oct 07 2005, Chen, Kenneth W wrote: > Jens Axboe wrote on Friday, October 07, 2005 12:24 AM > > I don't understand the need for this patch - the generic tagging is > only > > used if the SCSI LLD indicated it wanted it by issuing a > > scsi_activate_tcq(). So blk_queue_start_tag() is only called if the > LLD > > already did a scsi_activate_tcq(), and blk_queue_end_tag() is only > > called if the rq is block layer tagged. blk_queue_find_tag() is only > > used with direct use of scsi_find_tag(), a function that should (and > is) > > only usable by users of the generic tagging already. > > > > You beat me by a couple of minutes. I was about to say that the culprit > is in the qla2x00 driver where it unnecessarily activated generic blk > tag queuing by calling scsi_activate_tcq() and it never uses tag. > > > So please, a description of what problem you are trying to solve would > > be appreciated :-) > > It starts out with scsi_end_request being a fairly hot function in the > execution profile, then I noticed blk_queue_start/end_tag() are being > called but no actual consumer of using the tag. I'm trying to find a > way to avoid making these blk_queue_start/end_tag calls. I got the > answer > now. The proper way is to fix it in the scsi LLDD. Scratch this patch, > new patch to follow :-) Ok that makes more sense! But it's a little worrying that blk_queue_end_tag() would show up as hot in the profile, it is actually quite lean. -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
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