On Tue, Sep 1, 2015 at 5:29 PM, Wanpeng Li <wanpeng.li@xxxxxxxxxxx> wrote: > On 9/2/15 7:24 AM, David Matlack wrote: >> >> On Tue, Sep 1, 2015 at 3:58 PM, Wanpeng Li <wanpeng.li@xxxxxxxxxxx> wrote: <snip> >>> >>> Why this can happen? >> >> Ah, probably because I'm missing 9c8fd1ba220 (KVM: x86: optimize delivery >> of TSC deadline timer interrupt). I don't think the edge case exists in >> the latest kernel. > > > Yeah, hope we both(include Peter Kieser) can test against latest kvm tree to > avoid confusing. The reason to introduce the adaptive halt-polling toggle is > to handle the "edge case" as you mentioned above. So I think we can make > more efforts improve v4 instead. I will improve v4 to handle short halt > today. ;-) That's fine. It's just easier to convey my ideas with a patch. FYI the other reason for the toggle patch was to add the timer for kvm_vcpu_block, which I think is the only way to get dynamic halt-polling right. Feel free to work on top of v4! > <snip> >>> >>> Did you test your patch against a windows guest? >> >> I have not. I tested against a 250HZ linux guest to check how it performs >> against a ticking guest. Presumably, windows should be the same, but at a >> higher tick rate. Do you have a test for Windows? > > > I just test the idle vCPUs usage. > > > V4 for windows 10: > > +-----------------+----------------+-----------------------+ > | | | > | > | w/o halt-poll | w/ halt-poll | dynamic(v4) halt-poll > | > +-----------------+----------------+-----------------------+ > | | | > | > | ~2.1% | ~3.0% | ~2.4% > | > +-----------------+----------------+-----------------------+ I'm not seeing the same results with v4. With a 250HZ ticking guest I see 15% c0 with halt_poll_ns=2000000 and 1.27% with halt_poll_ns=0. Are you running one vcpu per pcpu? (The reason for the overhead: the new tracepoint shows each vcpu is alternating between 0 and 500 us.) > > V4 for linux guest: > > +-----------------+----------------+-------------------+ > | | | | > | w/o halt-poll | w/ halt-poll | dynamic halt-poll | > +-----------------+----------------+-------------------+ > | | | | > | ~0.9% | ~1.8% | ~1.2% | > +-----------------+----------------+-------------------+ > > > Regards, > Wanpeng Li -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
