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@joelfernandes.org
- Joel
Sebastian