On Thu, 2015-09-24 at 01:50 +0000, Wu, Feng wrote: > > -----Original Message----- > > From: George Dunlap [mailto:george.dun...@citrix.com]
> > This seems to me to be a cleaner design. It removes the need to > > modify > > any code on context-switch path. It moves modification of NDST and > > most > > modifications of SN closer to where I think they logically go. It > > reduces the number of unnecessary PI interrupts delivered to the > > hypervisor (by suppressing notifications most of the time spend in > > the > > hypervisor), and automatically deals with the "spurious interrupts > > during tasklet execution / vcpu offline lazy context switch" issue > > we > > were talking about with the other thread. > > One issue is the number of vmexits is far far bigger than the number > of > context switch. I test it for a quite short time and it shows there > are > 2910043 vmexits and 71733 context switch (only count the number in > __context_switch() since we only change the PI state in this > function). > If we change the PI state in each vmexit/vmentry, I am afraid this > will > hurt the performance. > Interesting. Hard to tell without actually trying, though. Personally, I'd agree with George and Jan that the vmexit solution is more self contained, and hence preferable. I don't really dislike the __context_switch() solution, though, and I'd be fine to live with it, especially considering these numbers. I guess the absolute best would be for you to prototype both, and try gathering some performance numbers for comparison... Is this asking too much? :-) Regards, Dario -- <<This happens because I choose it to happen!>> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
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