linux-kernel - Re: [PATCH] sched: correct testing need_resched in mutex_spin_on

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Message-ID: <BANLkTi=XTpYTZvetOUDgobRa_S4Cb=+syA@mail.gmail.com>
Date:	Tue, 7 Jun 2011 22:47:21 +0800
From:	Hillf Danton <dhillf@...il.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] sched: correct testing need_resched in mutex_spin_on_owner()

On Tue, Jun 7, 2011 at 10:40 PM, Peter Zijlstra <peterz@...radead.org> wrote:
> On Tue, 2011-06-07 at 22:36 +0800, Hillf Danton wrote:
>
>> If you are right, the following comment also in __mutex_lock_common()
>>
>>       for (;;) {
>>               struct task_struct *owner;
>>
>>               /*
>>                * If there's an owner, wait for it to either
>>                * release the lock or go to sleep.
>>                */
>>               owner = ACCESS_ONCE(lock->owner);
>>               if (owner && !mutex_spin_on_owner(lock, owner))
>>                       break;
>>
>> looks misleading too, but if owner is on this CPU, for what does we wait?
>
> huh, wtf!? it cannot be on this cpu, if it was we wouldn't be running
> the above code but whatever owner was doing.
>
> So my argument was, it cannot be on this cpu, therefore, by checking it
> is on a cpu, we check its on a different cpu.
>
> And I really don't see how any of that is related to the above.
>
Oh, it looks you are willing to rethink about testing need_resched?

thanks
           Hillf
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