On 03/27/2018 01:07 PM, Ingo Molnar wrote: > - To see at minimum stddev numbers, to make sure we are not looking at some weird > statistical artifact. (I also outlined a more robust measurement method.) > > - If the numbers are right, a CPU engineer should have a look if possible, > because frankly this effect is not expected and is not intuitive. Where global > pages can be used safely they are almost always an unconditional win. > Maybe we are missing some limitation or some interaction with PCID. > > Since we'll be using PCID even on Meltdown-fixed hardware, maybe the same negative > performance effect already exists on non-PTI kernels as well, we just never > noticed? Yep, totally agree. I'll do the more robust collection and also explore on "real" !PCID hardware. I also know the right CPU folks to go ask about this, I just want to do the second round of robust data collection before I bug them.
