Messages in this thread |  | | | Date | Wed, 30 Jun 2010 14:21:34 +0100 | | From | "Jan Beulich" <> | | Subject | Re: [PATCH 1/4, v2] x86: enlightenment for ticket spin locks - base implementation |
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>>> On 30.06.10 at 14:53, Jeremy Fitzhardinge <jeremy@goop.org> wrote: > On 06/30/2010 01:52 PM, Jan Beulich wrote: >> I fail to see that: Depending on the hypervisor's capabilities, the >> two main functions could be much smaller (potentially there wouldn't >> even be a need for the unlock hook in some cases), > > What mechanism are you envisaging in that case?
A simple yield is better than not doing anything at all.
>> The list really juts is needed to not pointlessly tickle CPUs that >> won't own the just released lock next anyway (or would own >> it, but meanwhile went for another one where they also decided >> to go into polling mode). > > Did you measure that it was a particularly common case which was worth > optimising for?
I didn't measure this particular case. But since the main problem with ticket locks is when (host) CPUs are overcommitted, it certainly is a bad idea to create even more load on the host than there already is (the more that these are bursts).
Jan
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