From: Andy Lutomirski <luto@kernel.org>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Stephen Rothwell <sfr@canb.auug.org.au>,
Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@elte.hu>,
"H. Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Linux-Next Mailing List <linux-next@vger.kernel.org>,
linux-kernel <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>
Subject: Re: linux-next: manual merge of the rcu tree with the tip tree
Date: Tue, 1 Aug 2017 06:43:14 -0700 [thread overview]
Message-ID: <CALCETrWO5g5HuNpxa4Phxg--fDPWpuCVDTVr-UfuzrK5wn-8dQ@mail.gmail.com> (raw)
In-Reply-To: <20170801040323.GP3730@linux.vnet.ibm.com>
On Mon, Jul 31, 2017 at 9:03 PM, Paul E. McKenney
<paulmck@linux.vnet.ibm.com> wrote:
> On Tue, Aug 01, 2017 at 12:04:05AM +0000, Mathieu Desnoyers wrote:
>> ----- On Jul 31, 2017, at 12:13 PM, Paul E. McKenney paulmck@linux.vnet.ibm.com wrote:
>>
> Thanx, Paul
>
> ------------------------------------------------------------------------
>
> commit fde19879b6bd1abc0c1d4d5f945efed61bf7eb8c
> Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
> Date: Fri Jul 28 16:40:40 2017 -0400
>
> membarrier: Expedited private command
>
> Implement MEMBARRIER_CMD_PRIVATE_EXPEDITED with IPIs using cpumask built
> from all runqueues for which current thread's mm is the same as the
> thread calling sys_membarrier. It executes faster than the non-expedited
> variant (no blocking). It also works on NOHZ_FULL configurations.
>
> Scheduler-wise, it requires a memory barrier before and after context
> switching between processes (which have different mm). The memory
> barrier before context switch is already present. For the barrier after
> context switch:
>
> * Our TSO archs can do RELEASE without being a full barrier. Look at
> x86 spin_unlock() being a regular STORE for example. But for those
> archs, all atomics imply smp_mb and all of them have atomic ops in
> switch_mm() for mm_cpumask().
I think that, on x86, context switches, even without mm changes, must
at least flush the store buffer (maybe SFENCE is okay) to avoid
visible inconsistency due to store-buffer forwarding.
Anyway, can you document whatever property you require with a comment
in switch_mm() or wherever you're finding that property so that future
arch changes don't break it?
> +static void membarrier_private_expedited(void)
> +{
> + int cpu;
> + bool fallback = false;
> + cpumask_var_t tmpmask;
> +
> + if (num_online_cpus() == 1)
> + return;
> +
> + /*
> + * Matches memory barriers around rq->curr modification in
> + * scheduler.
> + */
> + smp_mb(); /* system call entry is not a mb. */
> +
> + /*
> + * Expedited membarrier commands guarantee that they won't
> + * block, hence the GFP_NOWAIT allocation flag and fallback
> + * implementation.
> + */
> + if (!zalloc_cpumask_var(&tmpmask, GFP_NOWAIT)) {
> + /* Fallback for OOM. */
> + fallback = true;
> + }
> +
> + cpus_read_lock();
> + for_each_online_cpu(cpu) {
> + struct task_struct *p;
> +
> + /*
> + * Skipping the current CPU is OK even through we can be
> + * migrated at any point. The current CPU, at the point
> + * where we read raw_smp_processor_id(), is ensured to
> + * be in program order with respect to the caller
> + * thread. Therefore, we can skip this CPU from the
> + * iteration.
> + */
> + if (cpu == raw_smp_processor_id())
> + continue;
> + rcu_read_lock();
> + p = task_rcu_dereference(&cpu_rq(cpu)->curr);
> + if (p && p->mm == current->mm) {
I'm a bit surprised you're iterating all CPUs instead of just CPUs in
mm_cpumask().
next prev parent reply other threads:[~2017-08-01 13:43 UTC|newest]
Thread overview: 71+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-31 3:50 linux-next: manual merge of the rcu tree with the tip tree Stephen Rothwell
2017-07-31 16:13 ` Paul E. McKenney
2017-08-01 0:04 ` Mathieu Desnoyers
2017-08-01 4:03 ` Paul E. McKenney
2017-08-01 4:25 ` Mathieu Desnoyers
2017-08-01 16:31 ` Paul E. McKenney
2017-08-01 13:43 ` Andy Lutomirski [this message]
2017-08-01 13:58 ` Peter Zijlstra
2017-08-01 14:15 ` Peter Zijlstra
2017-08-01 14:17 ` Andy Lutomirski
2017-08-01 14:02 ` Mathieu Desnoyers
2017-08-01 14:15 ` Andy Lutomirski
2017-08-01 15:40 ` Mathieu Desnoyers
2017-08-01 21:36 ` Paul E. McKenney
-- strict thread matches above, loose matches on Subject: below --
2024-02-27 1:55 Stephen Rothwell
2022-04-06 2:45 Stephen Rothwell
2022-04-06 16:28 ` Paul E. McKenney
2022-02-21 18:17 broonie
2021-10-12 4:48 Stephen Rothwell
2021-10-13 16:31 ` Paul E. McKenney
2021-08-17 7:09 Stephen Rothwell
2021-06-23 5:33 Stephen Rothwell
2021-06-22 4:51 Stephen Rothwell
2021-06-22 4:47 Stephen Rothwell
2021-06-22 5:04 ` Stephen Rothwell
2021-06-22 17:10 ` Paul E. McKenney
2020-10-09 4:59 Stephen Rothwell
2020-07-29 6:23 Stephen Rothwell
2020-06-26 3:14 Stephen Rothwell
2020-06-25 2:44 Stephen Rothwell
2020-06-25 3:44 ` Paul E. McKenney
2020-06-24 3:04 Stephen Rothwell
2020-06-24 4:06 ` Paul E. McKenney
2020-05-29 6:22 Stephen Rothwell
2020-05-29 6:41 ` Stephen Rothwell
2020-05-29 14:15 ` Paul E. McKenney
2020-05-29 23:38 ` Stephen Rothwell
2020-03-25 3:08 Stephen Rothwell
2020-03-25 3:18 ` Paul E. McKenney
2020-03-25 21:31 ` Paul E. McKenney
2019-12-19 0:50 Stephen Rothwell
2019-12-19 1:27 ` Paul E. McKenney
2019-12-19 1:31 ` Paul E. McKenney
2019-12-19 8:41 ` Peter Zijlstra
2019-12-19 13:38 ` Paul E. McKenney
2019-12-16 23:37 Stephen Rothwell
2018-06-22 2:27 Stephen Rothwell
2018-06-26 19:33 ` Paul E. McKenney
2017-11-10 2:14 Stephen Rothwell
2017-08-22 4:13 Stephen Rothwell
2016-07-18 5:26 Stephen Rothwell
2016-07-19 3:00 ` Paul E. McKenney
2016-06-09 5:14 Stephen Rothwell
2016-06-09 15:59 ` Paul E. McKenney
2016-03-04 4:13 Stephen Rothwell
2016-03-04 15:04 ` Paul E. McKenney
2015-07-16 2:57 Stephen Rothwell
2015-05-07 3:56 Stephen Rothwell
2014-02-24 4:18 Stephen Rothwell
2014-02-24 4:42 ` Paul E. McKenney
2012-09-05 3:59 Stephen Rothwell
2012-09-05 16:39 ` Paul E. McKenney
2012-09-05 17:11 ` Peter Zijlstra
2012-08-23 3:01 Stephen Rothwell
2012-08-23 3:22 ` Paul E. McKenney
2012-08-22 4:27 Stephen Rothwell
2012-08-22 5:05 ` Paul E. McKenney
2012-08-22 4:27 Stephen Rothwell
2012-08-22 5:03 ` Paul E. McKenney
2011-06-20 4:47 Stephen Rothwell
2011-06-20 15:17 ` Paul E. McKenney
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