On 09/02/2012 09:59 PM, Rik van Riel wrote:
On 09/02/2012 06:12 AM, Gleb Natapov wrote:
On Thu, Aug 30, 2012 at 12:51:01AM +0530, Raghavendra K T wrote:
The idea of starting from next vcpu (source of yield_to + 1) seem to
work
well for overcomitted guest rather than using last boosted vcpu. We
can also
remove per VM variable with this approach.
Iteration for eligible candidate after this patch starts from vcpu
source+1
and ends at source-1 (after wrapping)
Thanks Nikunj for his quick verification of the patch.
Please let me know if this patch is interesting and makes sense.
This last_boosted_vcpu thing caused us trouble during attempt to
implement vcpu destruction. It is good to see it removed from this POV.
I like this implementation. It should achieve pretty much
the same as my old code, but without the downsides and without
having to keep the same amount of global state.
My theoretical understanding how it would help is,
|
V
T0 ------- T1
suppose there are 4 vcpus (v1..v4) out of 32/64 vcpus simpultaneously
enter directed yield handler,
if last_boosted_vcpu = i then v1 .. v4 will start from i, and there may
be some unnecessary attempts for directed yields.
We may not see such attempts with above patch. But again I agree that,
whole directed_yield stuff itself is very complicated because of
possibility of each vcpu in different state (running/pauseloop exited
while spinning/eligible) and how they are located w.r.t each other.
Here is the result I got for ebizzy, 32 vcpu guest 32 core PLE machine
for 1x 2x and 3x overcommits.
base = 3.5-rc5 kernel with ple handler improvements patches applied
patched = base + vcpuid patch
base stdev patched stdev %improvement
1x 1955.6250 39.8961 1863.3750 37.8302 -4.71716
2x 2475.3750 165.0307 3078.8750 341.9500 24.38014
3x 2071.5556 91.5370 2112.6667 56.6171 1.98455
Note:
I have to admit that, I am seeing very inconsistent results while
experimenting with 3.6-rc kernel (not specific to vcpuid patch but as a
whole) but not sure if it is some thing wrong in my config or should I
spend some time debugging. Anybody has observed same?
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