From: Peter Zijlstra <peterz@infradead.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: paulmck@linux.vnet.ibm.com, tj@kernel.org, mingo@redhat.com,
der.herr@hofr.at, dave@stgolabs.net, riel@redhat.com,
viro@ZenIV.linux.org.uk, torvalds@linux-foundation.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 6/6] stop_machine: optimize stop_work_alloc()
Date: Mon, 29 Jun 2015 10:56:46 +0200 [thread overview]
Message-ID: <20150629085646.GC3644@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20150626021526.GA5717@redhat.com>
On Fri, Jun 26, 2015 at 04:15:26AM +0200, Oleg Nesterov wrote:
> wait_event()/wake_up_all() in stop_work_alloc/stop_work_free logic
> is very suboptimal because of non-exclusive wakeups. So we add the
> wait_queue_func_t alloc_wake() helper which wakes the waiter up only
> a) if it actually waits for a stop_work in the "freed" cpumask, and
> b) only after we already set ->stop_owner = waiter.
>
> So if 2 stop_machine()'s race with each other, the loser will likely
> call schedule() only once and we will have a single wakeup.
So I think I can beat lockdep into submission (ugly but still) do we
want to use an actual per-cpu mutex instead?
next prev parent reply other threads:[~2015-06-29 8:56 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-26 2:14 [RFC PATCH 0/6] stop_machine: kill stop_cpus_mutex and stop_cpus_lock Oleg Nesterov
2015-06-26 2:15 ` [RFC PATCH 1/6] stop_machine: move cpu_stopper_task and stop_cpus_work into struct cpu_stopper Oleg Nesterov
2015-06-26 2:15 ` [RFC PATCH 2/6] stop_machine: don't do for_each_cpu() twice in queue_stop_cpus_work() Oleg Nesterov
2015-06-26 2:15 ` [RFC PATCH 3/6] stop_machine: introduce stop_work_alloc() and stop_work_free() Oleg Nesterov
2015-06-26 2:15 ` [RFC PATCH 4/6] stop_machine: kill stop_cpus_mutex Oleg Nesterov
2015-06-26 2:15 ` [RFC PATCH 5/6] stop_machine: change stop_two_cpus() just use stop_cpu(), kill lg_double_lock/unlock Oleg Nesterov
2015-06-26 2:15 ` [RFC PATCH 6/6] stop_machine: optimize stop_work_alloc() Oleg Nesterov
2015-06-29 8:56 ` Peter Zijlstra [this message]
2015-06-26 2:31 ` [RFC PATCH 0/6] stop_machine: kill stop_cpus_mutex and stop_cpus_lock Oleg Nesterov
2015-06-26 12:23 ` Peter Zijlstra
2015-06-26 20:46 ` Oleg Nesterov
2015-06-29 4:02 ` Oleg Nesterov
2015-06-29 8:51 ` Peter Zijlstra
2015-06-30 1:08 ` Oleg Nesterov
2015-06-29 8:49 ` Peter Zijlstra
2015-06-30 1:03 ` Oleg Nesterov
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