Messages in this thread | | | Date | Thu, 4 Nov 2004 10:16:47 +0100 | From | Jens Axboe <> | Subject | Re: blk_queue_congestion_threshold() |
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On Thu, Nov 04 2004, Nick Piggin wrote: > Chuck Ebbert wrote: > > Looking at this function in ll_rw_blk.c: > > > > > >static void blk_queue_congestion_threshold(struct request_queue *q) > >{ > > int nr; > > > > nr = q->nr_requests - (q->nr_requests / 8) + 1; > > if (nr > q->nr_requests) > > nr = q->nr_requests; > > q->nr_congestion_on = nr; > > > > nr = q->nr_requests - (q->nr_requests / 8) - 1; > > if (nr < 1) > > nr = 1; > > q->nr_congestion_off = nr; > >} > > > > > > Why are the "on" and "off" thresholds the same, i.e. shouldn't there be > > some > > They aren't the same, there is some hysteresis. > > >hysteresis? Con Kolivas posted a patch that changed the "off" threshold to > >"nr_requests - nr_requests/8 - nr_requests/16" and it was said to be > >better, > >but it never made it into mainline (it also changed get_request_wait() and > >that > >was never merged either): > > > > Patch was from Arjan. IIRC everyone agreed it looked good, and from > all the feedback I have seen it has worked well. Jens just may not > have had time to get it merged, or forgotten about it. > > It can probably at least go to -mm for now.
It should just go to Linus, imho. It just got lost, I'll send it out today.
> >--- patches/linux-2.6.9-rc4-ck1/drivers/block/ll_rw_blk.c 2004-10-12 > >12:25:09.798003278 +0200 > >+++ linux-2.6.9-rc4-ck1/drivers/block/ll_rw_blk.c 2004-10-12 > >12:25:42.959479479 +0200 > >@@ -100,7 +100,7 @@ > > nr = q->nr_requests; > > q->nr_congestion_on = nr; > > > >- nr = q->nr_requests - (q->nr_requests / 8) - 1; > >+ nr = q->nr_requests - (q->nr_requests / 8) - (q->nr_requests/16)- > >1; > > if (nr < 1) > > nr = 1; > > q->nr_congestion_off = nr; > > The stuff below this hunk is a different thing altogether, and should > not be merged. > > >@@ -1758,8 +1758,10 @@ > > { > > DEFINE_WAIT(wait); > > struct request *rq; > >+ struct io_context *ioc; > > > > generic_unplug_device(q); > >+ ioc = get_io_context(GFP_NOIO); > > do { > > struct request_list *rl = &q->rq; > > > >@@ -1769,7 +1771,6 @@ > > rq = get_request(q, rw, GFP_NOIO); > > > > if (!rq) { > >- struct io_context *ioc; > > > > io_schedule(); > > > >@@ -1779,12 +1780,11 @@ > > * up to a big batch of them for a small period > > time. > > * See ioc_batching, ioc_set_batching > > */ > >- ioc = get_io_context(GFP_NOIO); > > ioc_set_batching(q, ioc); > >- put_io_context(ioc); > > } > > finish_wait(&rl->wait[rw], &wait); > > } while (!rq); > >+ put_io_context(ioc); > > > > return rq; > > }
Yes this isn't valid, as discussed several times on linux-kernel.
-- Jens Axboe
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