On Sat, May 13, 2017 at 01:24:30AM +0000, Xu, Anthony wrote: > I think it is related to accel and platform, the result I gave before is for > q35 tcg, > > With the above change, I got below data > > Platform accel count of restoring A20 to 0 > Q35 kvm 96 > Q35 tcg 271 > PC kvm 3 > PC tcg 3
Okay, thanks. I think the number of a20 switches is due to differences in option rom execution interacting with the fact that some mode switches were occurring before SeaBIOS set call16_override(). > But I still see a lot of PORT_A20 accesses in QEMU as I expected Yes, but it should be possible to significantly reduce the number of outb() calls by limiting them to when A20 changes. This should also be useful to reduce the number of outb() calls needed to disable NMIs. I sent a patch series to the seabios mailing list to demonstrate the idea. -Kevin