lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Message-ID: <1511802882.2993.4.camel@wdc.com> Date: Mon, 27 Nov 2017 17:14:46 +0000 From: Bart Van Assche <Bart.VanAssche@....com> To: "dm-devel@...hat.com" <dm-devel@...hat.com>, "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>, "axboe@...com" <axboe@...com>, "ming.lei@...hat.com" <ming.lei@...hat.com>, "snitzer@...hat.com" <snitzer@...hat.com> CC: "hch@...radead.org" <hch@...radead.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "hare@...e.com" <hare@...e.com>, "osandov@...com" <osandov@...com> Subject: Re: [PATCH V2 1/5] dm-mpath: don't call blk_mq_delay_run_hw_queue() in case of BLK_STS_RESOURCE On Mon, 2017-11-27 at 13:07 +0800, Ming Lei wrote: > If .queue_rq() returns BLK_STS_RESOURCE, blk-mq will rerun the queue in > the three situations: > > 1) if BLK_MQ_S_SCHED_RESTART is set > - queue is rerun after one rq is completed, see blk_mq_sched_restart() > which is run from blk_mq_free_request() > > 2) run out of driver tag > - queue is rerun after one tag is freed > > 3) otherwise > - queue is run immediately in blk_mq_dispatch_rq_list() > > This random dealy of running hw queue is introduced by commit 6077c2d706097c0 > (dm rq: Avoid that request processing stalls sporadically), which claimed > one request processing stalling is fixed, but never explained the behind > idea, and it is a workaound at most. Even the question isn't explained by > anyone in recent discussion. > > Also calling blk_mq_delay_run_hw_queue() inside .queue_rq() is a horrible > hack because it makes BLK_MQ_S_SCHED_RESTART not working, and degrades I/O > peformance a lot. > > Finally this patch makes sure that dm-rq returns BLK_STS_RESOURCE to blk-mq > only when underlying queue is out of resource, so we switch to return > DM_MAPIO_DELAY_REQUEU if either MPATHF_QUEUE_IO or MPATHF_PG_INIT_REQUIRED > is set in multipath_clone_and_map(). Sorry but in my opinion the above description shows that you don't understand the dm-mpath driver completely. > diff --git a/drivers/md/dm-mpath.c b/drivers/md/dm-mpath.c > index c8faa2b85842..8fe3f45407ce 100644 > --- a/drivers/md/dm-mpath.c > +++ b/drivers/md/dm-mpath.c > @@ -484,9 +484,7 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq, > return DM_MAPIO_KILL; > } else if (test_bit(MPATHF_QUEUE_IO, &m->flags) || > test_bit(MPATHF_PG_INIT_REQUIRED, &m->flags)) { > - if (pg_init_all_paths(m)) > - return DM_MAPIO_DELAY_REQUEUE; > - return DM_MAPIO_REQUEUE; > + return DM_MAPIO_DELAY_REQUEUE; > } This patch removes a pg_init_all_paths() call but you don't explain why you think it is allowed to remove that call. Did you perhaps remove that call by mistake? Bart.
Powered by blists - more mailing lists