> 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.
If both TCG and KVM work by ignoring A20, why not remove all PORT_A20 access in SeaBios when CONFIG_DISABLE_A20 is not defined? Do you see any impact? -Anthony
