On 2019-04-25 12:45:58 [-0400], Joel Fernandes wrote: > On Wed, Apr 24, 2019 at 09:34:46AM +0200, Sebastian Andrzej Siewior wrote: > > In one of my rcutorture tests the TSC clocksource got marked unstable > > due to a large difference in the TSC value. I'm not sure if the guest > > run for a long time with disabled interrupts or if the host was very > > busy and didn't schedule the guest for some time. > > I took a look on the qemu/KVM options and decided to update the options: > > - Use kvm{32|64} as CPU. We could probably use `host' (like ARM does) > > for maximum available features but since we don't run any userland I'm > > not sure if it makes any difference. > > > > - Drop the "noapic" option, enable TSC deadline timer. There is no > > history why the APIC was disabled, I see no reason for it. The > > deadline timer is probably "nicer". > > I was wondering why the tsc deadline timer can't just be the default in the > kernel if it is "nicer" / "better" , and why does it need to be an option. The tsc-deadline=on part tells qemu to expose it. Otherwise the kernel can't use HW that isn't there. I added q35 as the machine which should pass enough sane default options. If this tsc-deadline timer is a problem we could probably drop it. The local-apic should work. > > - I didn't add a random HW device. It would make the random device ready > > earlier (not it doesn't complete the initialisation at all) but I > > doubt that there is any need for this. > > Didn't follow this point about "random HW device". It looks like there is no > part of the patch that matches this comment. There was no "random HW device" > needed for this change of the clocksource, so could you clarify what this means? I wanted to "upgrade" the kvm options and as part of it also add: -object rng-random,filename=/dev/urandom,id=rng0 -device virtio-rng-pci,rng=rng0 With that change you would see |random: crng init done during boot. Now you should end up with "only" |random: fast init done I mentioned it because I didn't see a reason why to do so. If someone has an idea why it would make sense for rcutorture to use it, I can add it. > Otherwise lgtm, thanks! > > Reviewed-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx> > > - Joel Sebastian