Messages in this thread | | | Date | Wed, 02 Jun 2010 05:51:14 +0300 | From | Avi Kivity <> | Subject | Re: [PATCH] use unfair spinlock when running on hypervisor. |
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On 06/01/2010 08:27 PM, Andi Kleen wrote: > On Tue, Jun 01, 2010 at 07:52:28PM +0300, Avi Kivity wrote: > >> We are running everything on NUMA (since all modern machines are now NUMA). >> At what scale do the issues become observable? >> > On Intel platforms it's visible starting with 4 sockets. >
Can you recommend a benchmark that shows bad behaviour? I'll run it with ticket spinlocks and Gleb's patch. I have a 4-way Nehalem-EX, presumably the huge number of threads will magnify the problem even more there.
>>>> I understand that reason and do not propose to get back to old spinlock >>>> on physical HW! But with virtualization performance hit is unbearable. >>>> >>>> >>> Extreme unfairness can be unbearable too. >>> >>> >> Well, the question is what happens first. In our experience, vcpu >> overcommit is a lot more painful. People will never see the NUMA >> unfairness issue if they can't use kvm due to the vcpu overcommit problem. >> > You really have to address both, if you don't fix them both > users will eventually into one of them and be unhappy. >
That's definitely the long term plan. I consider Gleb's patch the first step.
Do you have any idea how we can tackle both problems?
-- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.
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