From: Kirill Tkhai <tkhai@yandex.ru>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>, Ingo Molnar <mingo@redhat.com>
In-Reply-To: <20130618172805.GC16094@twins.programming.kicks-ass.net>
References: <1981131371569812@web20h.yandex.ru> <20130618172805.GC16094@twins.programming.kicks-ass.net>
Subject: Re: [PATCH 1/2] sched: Add schedule_(raw_)spin_unlock and schedule_(raw_)spin_unlock_irq
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Message-Id: <15591371577574@web20h.yandex.ru>
Date: Tue, 18 Jun 2013 21:46:14 +0400
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18.06.2013, 21:28, "Peter Zijlstra" <peterz@infradead.org>:
> On Tue, Jun 18, 2013 at 07:36:52PM +0400, Kirill Tkhai wrote:
>
>> ?Helpers for replacement repeating patterns:
>>
>> ?1)spin_unlock(lock);
>> ???schedule();
>> ?2)spin_unlock_irq(lock);
>> ???schedule();
>
> I just noticed this; the existing schedule_preempt_disabled() is
> equivalent to:
>
> ??preempt_enable()
> ??schedule()
> ??preempt_disable()
>
> So I somewhat expected these new primitives to be:
>
> ??spin_unlock()
> ??schedule()
> ??spin_lock()
>
> Now I haven't actually looked at the usage patch to see what the
> converted sites look like (thanks for adding that one though!).
>
> My OCD just triggered on the preemption and locked schedule calls having
> different semantics.

They have different semantic and different ending.

Many places (as you can see from the second patch) need additional actions
between schedule() and next spin_lock(). Several places don't do the second
lock.

Kirill
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