On Fri, Nov 07 2008, FUJITA Tomonori wrote: > On Thu, 6 Nov 2008 08:23:54 +0100 > Jens Axboe <jens.axboe@xxxxxxxxxx> wrote: > > > On Thu, Nov 06 2008, FUJITA Tomonori wrote: > > > On Mon, 3 Nov 2008 09:52:48 +0100 > > > Jens Axboe <jens.axboe@xxxxxxxxxx> wrote: > > > > > > > > In blk_del_timer(), there's no reason to test q->rq_timed_out_fn. If > > > > > the method pointer is NULL then req->deadline would be 0 anyway. In > > > > > addition, req->deadline should be set to 0 and the end of the routine, > > > > > just in case req gets requeued. > > > > > > > > > > In blk_add_timer(), the line > > > > > > > > > > expiry = round_jiffies(req->deadline); > > > > > > > > > > is not optimal. round_jiffies() will sometimes round a value _down_ to > > > > > the nearest second. But blk_rq_timed_out_timer() tests whether > > > > > req->deadline is in the past -- and if the deadline was rounded down > > > > > then this won't be true the first time through. You wind up getting an > > > > > unnecessary timer interrupt. Instead there should be a > > > > > round_jiffies_up() utility routine, and it should be used in both > > > > > blk_add_timer() and blk_rq_timed_out_timer(). > > > > > > > > Very good point, we do indeed want a round_jiffies_up() for this! > > > > > > Just out of curiosity, why do we need to use round_jiffies here? We > > > didn't do that for SCSI, right? > > > > We don't have to, but given that we don't care about exact timeouts, we > > may as well. It's not a new thing, we've done that since pretty much the > > beginning of the generic timeout development. > > I'm not sure that the users of the timeout feature can control exact > timeouts because the block layer doesn't let the users directly play > with the timer. elv_dequeue_request() is not the exact time that the > users want to start the timer. Instead, the block layer hides the > details behind the elevator (note that as I said before, I think that > it's the right thing). So the round_jiffies in the block layer doesn't > make sense to me. I prefer remove them instead of adding a bunch of > round_jiffies_up_* (I bet that some of them will never be used). I don't understand your concern, to be honest. We only need to round up once, and that is when we add/mod the timer. And we do that simply to play nice and group the timout with other timers, to save a bit of power. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
