Messages in this thread | | | Date | Thu, 26 Mar 2015 21:21:53 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 0/9] qspinlock stuff -v15 |
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On Wed, Mar 25, 2015 at 03:47:39PM -0400, Konrad Rzeszutek Wilk wrote: > Ah nice. That could be spun out as a seperate patch to optimize the existing > ticket locks I presume.
Yes I suppose we can do something similar for the ticket and patch in the right increment. We'd need to restructure the code a bit, but its not fundamentally impossible.
We could equally apply the head hashing to the current ticket implementation and avoid the current bitmap iteration.
> Now with the old pv ticketlock code an vCPU would only go to sleep once and > be woken up when it was its turn. With this new code it is woken up twice > (and twice it goes to sleep). With an overcommit scenario this would imply > that we will have at least twice as many VMEXIT as with the previous code.
An astute observation, I had not considered that.
> I presume when you did benchmarking this did not even register? Thought > I wonder if it would if you ran the benchmark for a week or so.
You presume I benchmarked :-) I managed to boot something virt and run hackbench in it. I wouldn't know a representative virt setup if I ran into it.
The thing is, we want this qspinlock for real hardware because its faster and I really want to avoid having to carry two spinlock implementations -- although I suppose that if we really really have to we could.
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