Thank you for the investigation. Now I have a solid reason to postpone the Win10 upgrade.
On Sat, May 14, 2016, 11:21 AM Abdulla Bubshait <[email protected]> wrote: > So for the people having problem with Heroes of the Storm or > StarCraft2 on Windows 10, > here is what I have been able to piece together. > > Those two games use a ton of branch tracing code. Specifically, they > enable and access > LBR registers (part of the Intel MSRs). The windows 10 code portion > for these games > seems to include a ton of LBR reads. Since these branch traces are > mainly for code > debugging purposes I personally believe that they were used to debug > win10 code for > these games and were forgotten. LBRs themselves don't hurt performance > much, although > having all those needless register reads can't be that beneficial. > > KVM does not support LBR. So without the ignore_msrs the game would > just crash. But > even if KVM simply returned 0 that is still a relatively expensive > process when compared > to a simple register read in native. Even if KVM were to implement LBR > that would only > make things worse because any implementation would cost more than a > simple return 0. > > With my limited knowledge of how KVM works I do not see how one can make a > host > respond to guests hammering LBR requests without taking a performance > hit, even if > they don't give the correct response. > > So it seems the only way to fix this performance issue is to have > Blizzard take out the > offending code in an upcoming patch. I feel the code was left in there > in error as at the > end of the day it's main purpose is debugging and shouldn't be active > in a game where > performance really matters. The question is how likely it is that > Blizzard will actually fix > this problem seeing as it really effects only a tiny subset of their user > base. > > I really wish I had a proper fix to the problem, but it seems that > getting these games to > run in VM preperly means avoiding win10. >
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