Re: [PATCH v4 2/3] locking/mutex: Enable optimistic spinning of woken task in wait queue

[Waiman Long]

On 08/08/2016 01:29 PM, Peter Zijlstra wrote:
> On Mon, Jul 18, 2016 at 04:39:25PM -0400, Waiman Long wrote:
> > Ding Tianhong reported a live-lock situation where a constant stream
> > of incoming optimistic spinners blocked a task in the wait list from
> > getting the mutex.
> >
> > This patch attempts to fix this live-lock condition by enabling the
> > woken task in the wait queue to enter into an optimistic spinning
> > loop itself in parallel with the regular spinners in the OSQ. This
> > should prevent the live-lock condition from happening.
> No, two spinners are not in fact starvation proof. It makes the reported
> life-lock scenario much less likely, but it does not guarantee anything.

Yes, I should have said reducing the chance of live-locking.

> > +		/*
> > +		 * Optimistically spinning on the mutex without the wait lock
> There should either be a '.' at the end of that line, or the next line
> should not start with a capital.
>
> Also, I don't see how the two sentences are related, should they be in
> the same paragraph?

Sorry for the missing '.', and I will split it into 2 paragraphs.

Cheers,
Longman