Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752026AbbD0CLZ (ORCPT ); Sun, 26 Apr 2015 22:11:25 -0400 Received: from mga01.intel.com ([192.55.52.88]:3603 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751769AbbD0CLX (ORCPT ); Sun, 26 Apr 2015 22:11:23 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.11,654,1422950400"; d="scan'208";a="701216226" Date: Mon, 27 Apr 2015 10:12:49 +0800 From: Yuanhan Liu To: NeilBrown Cc: linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/2] md/raid5: split wait_for_stripe and introduce wait_for_quiesce Message-ID: <20150427021249.GG17176@yliu-dev.sh.intel.com> References: <1429882744-22655-1-git-send-email-yuanhan.liu@linux.intel.com> <20150427101024.2ae8edc1@notabene.brown> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20150427101024.2ae8edc1@notabene.brown> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 7042 Lines: 189 On Mon, Apr 27, 2015 at 10:10:24AM +1000, NeilBrown wrote: > On Fri, 24 Apr 2015 21:39:03 +0800 Yuanhan Liu > wrote: > > > If I read code correctly, current wait_for_stripe actually has 2 usage: > > > > - wait for there is enough free stripe cache, triggered when > > get_free_stripe() failed. This is what wait_for_stripe intend > > for literally. > > > > - wait for quiesce == 0 or > > active_aligned_reads == 0 && active_stripes == 0 > > > > It has nothing to do with wait_for_stripe literally, and releasing > > an active stripe won't actually wake them up. On the contrary, wake_up > > from under this case won't actually wake up the process waiting for > > an free stripe being available. > > I disagree. Releasing an active stripe *will* (or *can*) wake up that third > case, as it decrements "active_stripes" which will eventually reach zero. > > I don't think your new code will properly wake up a process which is waiting > for "active_stripes == 0". Right, and thanks for pointing it out. So, is this enough? --- diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c index 2d8fcc1..3f23035 100644 --- a/drivers/md/raid5.c +++ b/drivers/md/raid5.c @@ -383,6 +383,9 @@ static void release_inactive_stripe_list(struct r5conf *conf, } } } + + if (!atomic_read(&conf->active_stripes)) + wake_up(&conf->wait_for_quiesce); } /* should hold conf->device_lock already */ Or, should I put it a bit ahead, trying to invoke wake_up(&conf->wait_for_quiesce) after each atomic_dec(&conf->active_stripes)? if (atomic_dec_return(&conf->active_stripes) == 0) wake_up(&conf->wait_for_quiesce); > > > > > Hence, we'd better split wait_for_stripe, and here I introduce > > wait_for_quiesce for the second usage. The name may not well taken, or > > even taken wrongly. Feel free to correct me then. > > > > This is also a prepare patch for next patch: make wait_for_stripe > > exclusive. > > I think you have this commit description upside down :-) > > The real motivation is that you are seeing contention on some spinlock and so > you want to split 'wait_for_stripe' up in to multiple wait_queues so that you > can use exclusive wakeup. As this is the main motivation, it should be > stated first. > > Then explain that 'wait_for_stripe' is used to wait for the array to enter or > leave the quiescent state, and also to wait for an available stripe in each > of the hash lists. > > So this patch splits the first usage off into a separate wait_queue, and the > next patch will split the second usage into one waitqueue for each hash value. > > Then explain just is what is needed for that first step. > > When you put it that way around, the patch makes lots of sense. It does, and thanks! > > So: could you please resubmit with the description the right way around, and To make sure I followed you correctly, my patch order is correct(I mean, split lock first, and make wait_for_stripe per lock hash and exclusive second), and what I need to do is re-writing the commit log as you suggested, and fixing all issues you pointed out. Right? --yliu > with an appropriate wakeup call to ensure raid5_quiesce is woken up when > active_stripes reaches zero? > > Thanks, > NeilBrown > > > > > > Signed-off-by: Yuanhan Liu > > --- > > drivers/md/raid5.c | 13 +++++++------ > > drivers/md/raid5.h | 1 + > > 2 files changed, 8 insertions(+), 6 deletions(-) > > > > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c > > index 9716319..b7e385f 100644 > > --- a/drivers/md/raid5.c > > +++ b/drivers/md/raid5.c > > @@ -667,7 +667,7 @@ get_active_stripe(struct r5conf *conf, sector_t sector, > > spin_lock_irq(conf->hash_locks + hash); > > > > do { > > - wait_event_lock_irq(conf->wait_for_stripe, > > + wait_event_lock_irq(conf->wait_for_quiesce, > > conf->quiesce == 0 || noquiesce, > > *(conf->hash_locks + hash)); > > sh = __find_stripe(conf, sector, conf->generation - previous); > > @@ -4725,7 +4725,7 @@ static void raid5_align_endio(struct bio *bi, int error) > > raid_bi, 0); > > bio_endio(raid_bi, 0); > > if (atomic_dec_and_test(&conf->active_aligned_reads)) > > - wake_up(&conf->wait_for_stripe); > > + wake_up(&conf->wait_for_quiesce); > > return; > > } > > > > @@ -4820,7 +4820,7 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio) > > align_bi->bi_iter.bi_sector += rdev->data_offset; > > > > spin_lock_irq(&conf->device_lock); > > - wait_event_lock_irq(conf->wait_for_stripe, > > + wait_event_lock_irq(conf->wait_for_quiesce, > > conf->quiesce == 0, > > conf->device_lock); > > atomic_inc(&conf->active_aligned_reads); > > @@ -5659,7 +5659,7 @@ static int retry_aligned_read(struct r5conf *conf, struct bio *raid_bio) > > bio_endio(raid_bio, 0); > > } > > if (atomic_dec_and_test(&conf->active_aligned_reads)) > > - wake_up(&conf->wait_for_stripe); > > + wake_up(&conf->wait_for_quiesce); > > return handled; > > } > > > > @@ -6390,6 +6390,7 @@ static struct r5conf *setup_conf(struct mddev *mddev) > > goto abort; > > spin_lock_init(&conf->device_lock); > > seqcount_init(&conf->gen_lock); > > + init_waitqueue_head(&conf->wait_for_quiesce); > > init_waitqueue_head(&conf->wait_for_stripe); > > init_waitqueue_head(&conf->wait_for_overlap); > > INIT_LIST_HEAD(&conf->handle_list); > > @@ -7413,7 +7414,7 @@ static void raid5_quiesce(struct mddev *mddev, int state) > > * active stripes can drain > > */ > > conf->quiesce = 2; > > - wait_event_cmd(conf->wait_for_stripe, > > + wait_event_cmd(conf->wait_for_quiesce, > > atomic_read(&conf->active_stripes) == 0 && > > atomic_read(&conf->active_aligned_reads) == 0, > > unlock_all_device_hash_locks_irq(conf), > > @@ -7427,7 +7428,7 @@ static void raid5_quiesce(struct mddev *mddev, int state) > > case 0: /* re-enable writes */ > > lock_all_device_hash_locks_irq(conf); > > conf->quiesce = 0; > > - wake_up(&conf->wait_for_stripe); > > + wake_up(&conf->wait_for_quiesce); > > wake_up(&conf->wait_for_overlap); > > unlock_all_device_hash_locks_irq(conf); > > break; > > diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h > > index 7dc0dd8..fab53a3 100644 > > --- a/drivers/md/raid5.h > > +++ b/drivers/md/raid5.h > > @@ -508,6 +508,7 @@ struct r5conf { > > struct list_head inactive_list[NR_STRIPE_HASH_LOCKS]; > > atomic_t empty_inactive_list_nr; > > struct llist_head released_stripes; > > + wait_queue_head_t wait_for_quiesce; > > wait_queue_head_t wait_for_stripe; > > wait_queue_head_t wait_for_overlap; > > unsigned long cache_state; > -- 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/