Re: [PATCH v6 5/6] MCS Lock: Restructure the MCS lock defines andlocking code into its own file

[Jason Low]

On Fri, 2013-09-27 at 08:02 +0200, Ingo Molnar wrote:
> * Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> wrote:
> 
> > > If we prefer to optimize this a bit though, perhaps we can first move 
> > > the node->lock = 0 so that it gets executed after the "if (likely(prev 
> > > == NULL)) {}" code block and then delete "node->lock = 1" inside the 
> > > code block.
> > 
> > I suppose we can save one single assignment. The gain is probably not 
> > noticeable as once we set node->next to NULL, node->locked is likely in 
> > local cache line and the assignment operation is cheap.
> 
> Would be nice to have this as a separate, add-on patch. Every single 
> instruction removal that has no downside is an upside!
> 
> You can add a comment that explains it.

Yup, especially a spin lock (and one that I have found to be be used
very frequently when running workloads on big machines).

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