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From: Aubrey Li <aubrey.intel@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Joel Fernandes <joel@joelfernandes.org>,
	"Hyser,Chris" <chris.hyser@oracle.com>,
	Josh Don <joshdon@google.com>, Ingo Molnar <mingo@kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Valentin Schneider <valentin.schneider@arm.com>,
	Mel Gorman <mgorman@suse.de>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 04/19] sched: Prepare for Core-wide rq->lock
Date: Thu, 29 Apr 2021 16:03:30 +0800	[thread overview]
Message-ID: <CAERHkrsC9rC4Jrkz8r-7kp4SFPM6aU+EHN+Y+uQiTuPG5S72bA@mail.gmail.com> (raw)
In-Reply-To: <20210422123308.196692074@infradead.org>

On Thu, Apr 22, 2021 at 8:39 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> When switching on core-sched, CPUs need to agree which lock to use for
> their RQ.
>
> The new rule will be that rq->core_enabled will be toggled while
> holding all rq->__locks that belong to a core. This means we need to
> double check the rq->core_enabled value after each lock acquire and
> retry if it changed.
>
> This also has implications for those sites that take multiple RQ
> locks, they need to be careful that the second lock doesn't end up
> being the first lock.
>
> Verify the lock pointer after acquiring the first lock, because if
> they're on the same core, holding any of the rq->__lock instances will
> pin the core state.
>
> While there, change the rq->__lock order to CPU number, instead of rq
> address, this greatly simplifies the next patch.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> ---
>  kernel/sched/core.c  |   48 ++++++++++++++++++++++++++++++++++++++++++++++--
>  kernel/sched/sched.h |   41 +++++++++++------------------------------
>  2 files changed, 57 insertions(+), 32 deletions(-)
>
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
----snip----
> @@ -199,6 +224,25 @@ void raw_spin_rq_unlock(struct rq *rq)
>         raw_spin_unlock(rq_lockp(rq));
>  }
>
> +#ifdef CONFIG_SMP
> +/*
> + * double_rq_lock - safely lock two runqueues
> + */
> +void double_rq_lock(struct rq *rq1, struct rq *rq2)
> +{
> +       lockdep_assert_irqs_disabled();
> +
> +       if (rq1->cpu > rq2->cpu)

It's still a bit hard for me to digest this function, I guess using (rq->cpu)
can't guarantee the sequence of locking when coresched is enabled.

- cpu1 and cpu7 shares lockA
- cpu2 and cpu8 shares lockB

double_rq_lock(1,8) leads to lock(A) and lock(B)
double_rq_lock(7,2) leads to lock(B) and lock(A)

change to below to avoid ABBA?
+       if (__rq_lockp(rq1) > __rq_lockp(rq2))

Please correct me if I was wrong.

Thanks,
-Aubrey

> +               swap(rq1, rq2);
> +
> +       raw_spin_rq_lock(rq1);
> +       if (rq_lockp(rq1) == rq_lockp(rq2))
> +               return;
> +
> +       raw_spin_rq_lock_nested(rq2, SINGLE_DEPTH_NESTING);
> +}
> +#endif
> +

  parent reply	other threads:[~2021-04-29  8:03 UTC|newest]

Thread overview: 103+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-22 12:04 [PATCH 00/19] sched: Core Scheduling Peter Zijlstra
2021-04-22 12:05 ` [PATCH 01/19] sched/fair: Add a few assertions Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-05-13  8:56     ` Ning, Hongyu
2021-04-22 12:05 ` [PATCH 02/19] sched: Provide raw_spin_rq_*lock*() helpers Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 03/19] sched: Wrap rq::lock access Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 04/19] sched: Prepare for Core-wide rq->lock Peter Zijlstra
2021-04-24  1:22   ` Josh Don
2021-04-26  8:31     ` Peter Zijlstra
2021-04-26 22:21       ` Josh Don
2021-04-27 17:10         ` Don Hiatt
2021-04-27 23:35           ` Josh Don
2021-04-28  1:03             ` Aubrey Li
2021-04-28  6:05               ` Aubrey Li
2021-04-28 10:57                 ` Aubrey Li
2021-04-28 16:41                   ` Don Hiatt
2021-04-29 20:48                     ` Josh Don
2021-04-29 21:09                       ` Don Hiatt
2021-04-29 23:22                         ` Josh Don
2021-04-30 16:18                           ` Don Hiatt
2021-04-30  8:26                         ` Aubrey Li
2021-04-28 16:04             ` Don Hiatt
2021-04-27 23:30         ` Josh Don
2021-04-28  9:13           ` Peter Zijlstra
2021-04-28 10:35             ` Aubrey Li
2021-04-28 11:03               ` Peter Zijlstra
2021-04-28 14:18                 ` Paul E. McKenney
2021-04-29 20:11             ` Josh Don
2021-05-03 19:17               ` Peter Zijlstra
2021-04-28  7:13         ` Peter Zijlstra
2021-04-28  6:02   ` Aubrey Li
2021-04-29  8:03   ` Aubrey Li [this message]
2021-04-29 20:39     ` Josh Don
2021-04-30  8:20       ` Aubrey Li
2021-04-30  8:48         ` Josh Don
2021-04-30 14:15           ` Aubrey Li
2021-05-04  7:38       ` Peter Zijlstra
2021-05-05 16:20         ` Don Hiatt
2021-05-06 10:25           ` Peter Zijlstra
2021-05-07  9:50   ` [PATCH v2 " Peter Zijlstra
2021-05-08  8:07     ` Aubrey Li
2021-05-12  9:07       ` Peter Zijlstra
2021-04-22 12:05 ` [PATCH 05/19] sched: " Peter Zijlstra
2021-05-07  9:50   ` [PATCH v2 " Peter Zijlstra
2021-05-12 10:28     ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 06/19] sched: Optimize rq_lockp() usage Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 07/19] sched: Allow sched_core_put() from atomic context Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 08/19] sched: Introduce sched_class::pick_task() Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 09/19] sched: Basic tracking of matching tasks Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 10/19] sched: Add core wide task selection and scheduling Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 11/19] sched/fair: Fix forced idle sibling starvation corner case Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Vineeth Pillai
2021-04-22 12:05 ` [PATCH 12/19] sched: Fix priority inversion of cookied task with sibling Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Joel Fernandes (Google)
2021-04-22 12:05 ` [PATCH 13/19] sched/fair: Snapshot the min_vruntime of CPUs on force idle Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Joel Fernandes (Google)
2021-04-22 12:05 ` [PATCH 14/19] sched: Trivial forced-newidle balancer Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 15/19] sched: Migration changes for core scheduling Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Aubrey Li
2021-04-22 12:05 ` [PATCH 16/19] sched: Trivial core scheduling cookie management Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 17/19] sched: Inherit task cookie on fork() Peter Zijlstra
2021-05-10 16:06   ` Joel Fernandes
2021-05-10 16:22     ` Chris Hyser
2021-05-10 20:47       ` Joel Fernandes
2021-05-10 21:38         ` Chris Hyser
2021-05-12  9:05           ` Peter Zijlstra
2021-05-12 20:20             ` Josh Don
2021-05-12 21:07               ` Don Hiatt
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 18/19] sched: prctl() core-scheduling interface Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Chris Hyser
2021-06-14 23:36   ` [PATCH 18/19] " Josh Don
2021-06-15 11:31     ` Joel Fernandes
2021-08-05 16:53   ` Eugene Syromiatnikov
2021-08-05 17:00     ` Peter Zijlstra
2021-08-17 15:15   ` Eugene Syromiatnikov
2021-08-17 15:52     ` Peter Zijlstra
2021-08-17 23:17       ` Eugene Syromiatnikov
2021-08-19 11:09         ` [PATCH] sched: Fix Core-wide rq->lock for uninitialized CPUs Peter Zijlstra
2021-08-19 15:50           ` Tao Zhou
2021-08-19 16:19           ` Eugene Syromiatnikov
2021-08-20  0:18           ` Josh Don
2021-08-20 10:02             ` Peter Zijlstra
2021-08-23  9:07           ` [tip: sched/urgent] " tip-bot2 for Peter Zijlstra
2021-04-22 12:05 ` [PATCH 19/19] kselftest: Add test for core sched prctl interface Peter Zijlstra
2021-05-12 10:28   ` [tip: sched/core] " tip-bot2 for Chris Hyser
2021-04-22 16:43 ` [PATCH 00/19] sched: Core Scheduling Don Hiatt
2021-04-22 17:29   ` Peter Zijlstra
2021-04-30  6:47 ` Ning, Hongyu
2021-05-06 10:29   ` Peter Zijlstra
2021-05-06 12:53     ` Ning, Hongyu
2021-05-07 18:02 ` Joel Fernandes
2021-05-10 16:16 ` Vincent Guittot
2021-05-11  7:00   ` Vincent Guittot

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