Re: [PATCH] Convert powerpc simple spinlocks into ticket locks

From: Torsten Duwe
Date: Fri Feb 07 2014 - 07:57:07 EST

On Fri, Feb 07, 2014 at 11:45:30AM +0100, Peter Zijlstra wrote:
> That might need to be lhz too, I'm confused on all the load variants.


> > unlock:
> > lhz %0, 0, &tail
> > addic %0, %0, 1

No carry with this one, I'd say.
Besides, unlock increments the head.

> > lwsync
> > sth %0, 0, &tail
> >

Given the beauty and simplicity of this, may I ask Ingo:
you signed off 314cdbefd1fd0a7acf3780e9628465b77ea6a836;
can you explain why head and tail must live on the same cache
line? Or is it just a space saver? I just ported it to ppc,
I didn't think about alternatives.

What about

atomic_t tail;
volatile int head; ?

Admittedly, that's usually 8 bytes instead of 4...


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