From: Kent Overstreet <kent.overstreet@gmail.com>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will.deacon@arm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Waiman Long <waiman.long@hpe.com>, Jason Low <jason.low2@hpe.com>,
Ding Tianhong <dingtianhong@huawei.com>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Imre Deak <imre.deak@intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
Terry Rudd <terry.rudd@hpe.com>,
"Paul E. McKenney" <paulmck@us.ibm.com>,
Jason Low <jason.low2@hp.com>,
Chris Wilson <chris@chris-wilson.co.uk>,
Daniel Vetter <daniel.vetter@ffwll.ch>,
axboe@fb.com, linux-bcache@vger.kernel.org
Subject: Re: ciao set_task_state() (was Re: [PATCH -v4 6/8] locking/mutex: Restructure wait loop)
Date: Mon, 24 Oct 2016 05:26:39 -0800 [thread overview]
Message-ID: <20161024132639.vrbcfrnorbovmkaj@kmo-pixel> (raw)
In-Reply-To: <20161024015726.GA26130@linux-80c1.suse>
On Sun, Oct 23, 2016 at 06:57:26PM -0700, Davidlohr Bueso wrote:
> On Wed, 19 Oct 2016, Peter Zijlstra wrote:
>
> > Subject: sched: Better explain sleep/wakeup
> > From: Peter Zijlstra <peterz@infradead.org>
> > Date: Wed Oct 19 15:45:27 CEST 2016
> >
> > There were a few questions wrt how sleep-wakeup works. Try and explain
> > it more.
> >
> > Requested-by: Will Deacon <will.deacon@arm.com>
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> > ---
> > include/linux/sched.h | 52 ++++++++++++++++++++++++++++++++++----------------
> > kernel/sched/core.c | 15 +++++++-------
> > 2 files changed, 44 insertions(+), 23 deletions(-)
> >
> > --- a/include/linux/sched.h
> > +++ b/include/linux/sched.h
> > @@ -262,20 +262,9 @@ extern char ___assert_task_state[1 - 2*!
> > #define set_task_state(tsk, state_value) \
> > do { \
> > (tsk)->task_state_change = _THIS_IP_; \
> > - smp_store_mb((tsk)->state, (state_value)); \
> > + smp_store_mb((tsk)->state, (state_value)); \
> > } while (0)
> >
> > -/*
> > - * set_current_state() includes a barrier so that the write of current->state
> > - * is correctly serialised wrt the caller's subsequent test of whether to
> > - * actually sleep:
> > - *
> > - * set_current_state(TASK_UNINTERRUPTIBLE);
> > - * if (do_i_need_to_sleep())
> > - * schedule();
> > - *
> > - * If the caller does not need such serialisation then use __set_current_state()
> > - */
> > #define __set_current_state(state_value) \
> > do { \
> > current->task_state_change = _THIS_IP_; \
> > @@ -284,11 +273,19 @@ extern char ___assert_task_state[1 - 2*!
> > #define set_current_state(state_value) \
> > do { \
> > current->task_state_change = _THIS_IP_; \
> > - smp_store_mb(current->state, (state_value)); \
> > + smp_store_mb(current->state, (state_value)); \
> > } while (0)
> >
> > #else
> >
> > +/*
> > + * @tsk had better be current, or you get to keep the pieces.
>
> That reminds me we were getting rid of the set_task_state() calls. Bcache was
> pending, being only user in the kernel that doesn't actually use current; but
> instead breaks newly (yet blocked/uninterruptible) created garbage collection
> kthread. I cannot figure out why this is done (ie purposely accounting the
> load avg. Furthermore gc kicks in in very specific scenarios obviously, such
> as as by the allocator task, so I don't see why bcache gc should want to be
> interruptible.
>
> Kent, Jens, can we get rid of this?
>
> diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> index 76f7534d1dd1..6e3c358b5759 100644
> --- a/drivers/md/bcache/btree.c
> +++ b/drivers/md/bcache/btree.c
> @@ -1798,7 +1798,6 @@ int bch_gc_thread_start(struct cache_set *c)
> if (IS_ERR(c->gc_thread))
> return PTR_ERR(c->gc_thread);
>
> - set_task_state(c->gc_thread, TASK_INTERRUPTIBLE);
> return 0;
> }
Actually, that code looks broken, or at least stupid. Let me do a proper fix...
next prev parent reply other threads:[~2016-10-24 13:26 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-07 14:52 [PATCH -v4 0/8] locking/mutex: Rewrite basic mutex Peter Zijlstra
2016-10-07 14:52 ` [PATCH -v4 1/8] locking/drm: Kill mutex trickery Peter Zijlstra
2016-10-07 15:43 ` Peter Zijlstra
2016-10-07 15:58 ` Linus Torvalds
2016-10-07 16:13 ` Peter Zijlstra
2016-10-07 21:58 ` Waiman Long
2016-10-08 11:58 ` Thomas Gleixner
2016-10-08 14:01 ` Peter Zijlstra
2016-10-08 14:11 ` Thomas Gleixner
2016-10-08 16:42 ` Peter Zijlstra
2016-11-09 10:38 ` Peter Zijlstra
2016-10-18 12:48 ` Peter Zijlstra
2016-10-18 12:57 ` Peter Zijlstra
2016-11-11 11:22 ` Daniel Vetter
2016-11-11 11:38 ` Peter Zijlstra
2016-11-12 10:58 ` Ingo Molnar
2016-11-14 14:04 ` Peter Zijlstra
2016-11-14 14:27 ` Ingo Molnar
2016-10-18 12:57 ` Chris Wilson
2016-10-07 14:52 ` [PATCH -v4 2/8] locking/mutex: Rework mutex::owner Peter Zijlstra
2016-10-12 17:59 ` Davidlohr Bueso
2016-10-12 19:52 ` Jason Low
2016-10-13 15:18 ` Will Deacon
2016-10-07 14:52 ` [PATCH -v4 3/8] locking/mutex: Kill arch specific code Peter Zijlstra
2016-10-07 14:52 ` [PATCH -v4 4/8] locking/mutex: Allow MUTEX_SPIN_ON_OWNER when DEBUG_MUTEXES Peter Zijlstra
2016-10-07 14:52 ` [PATCH -v4 5/8] locking/mutex: Add lock handoff to avoid starvation Peter Zijlstra
2016-10-13 15:14 ` Will Deacon
2016-10-17 9:22 ` Peter Zijlstra
2016-10-17 18:45 ` Waiman Long
2016-10-17 19:07 ` Waiman Long
2016-10-18 13:02 ` Peter Zijlstra
2016-10-18 12:36 ` Peter Zijlstra
2016-12-27 13:55 ` Chris Wilson
2017-01-09 11:52 ` [PATCH] locking/mutex: Clear mutex-handoff flag on interrupt Chris Wilson
2017-01-11 16:43 ` Peter Zijlstra
2017-01-11 16:57 ` Chris Wilson
2017-01-12 20:58 ` Chris Wilson
2016-10-07 14:52 ` [PATCH -v4 6/8] locking/mutex: Restructure wait loop Peter Zijlstra
2016-10-13 15:17 ` Will Deacon
2016-10-17 10:44 ` Peter Zijlstra
2016-10-17 13:24 ` Peter Zijlstra
2016-10-17 13:45 ` Boqun Feng
2016-10-17 15:49 ` Peter Zijlstra
2016-10-19 17:34 ` Peter Zijlstra
2016-10-24 1:57 ` ciao set_task_state() (was Re: [PATCH -v4 6/8] locking/mutex: Restructure wait loop) Davidlohr Bueso
2016-10-24 13:26 ` Kent Overstreet [this message]
2016-10-24 14:27 ` Kent Overstreet
2016-10-25 16:55 ` Eric Wheeler
2016-10-25 17:45 ` Kent Overstreet
2016-10-17 23:16 ` [PATCH -v4 6/8] locking/mutex: Restructure wait loop Waiman Long
2016-10-18 13:14 ` Peter Zijlstra
2016-10-07 14:52 ` [PATCH -v4 7/8] locking/mutex: Simplify some ww_mutex code in __mutex_lock_common() Peter Zijlstra
2016-10-07 14:52 ` [PATCH -v4 8/8] locking/mutex: Enable optimistic spinning of woken waiter Peter Zijlstra
2016-10-13 15:28 ` Will Deacon
2016-10-17 9:32 ` Peter Zijlstra
2016-10-17 23:21 ` Waiman Long
2016-10-18 12:19 ` Peter Zijlstra
2016-10-07 15:20 ` [PATCH -v4 0/8] locking/mutex: Rewrite basic mutex Linus Torvalds
2016-10-11 18:42 ` Jason Low
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