Gleb Natapov wrote:
On Tue, Jul 22, 2008 at 08:20:41PM -0500, Anthony Liguori wrote:
Currently both in-kernel PIT and even the in kernel irqchips are not
100% bullet proof.
Of course this code is a hack, Gleb Natapov has send better fix for
PIT/RTC to qemu list.
Can you look into them:
http://www.mail-archive.com/[email protected]/msg01181.html
Paul Brook's initial feedback is still valid. It causes quite a lot of
churn and may not jive well with a virtual time base. An advantage to
the current -tdf patch is that it's more contained. I don't think
either approach is going to get past Paul in it's current form.
Yes, my patch causes a lot of churn because it changes widely used API.
Indeed.
But the time drift fix itself is contained to PIT/RTC code only. The
last patch series I've sent disables time drift fix if virtual time base
is enabled as Paul requested. There was no further feedback from him.
I think there's a healthy amount of scepticism about whether tdf really
is worth it. This is why I suggested that we need to better quantify
exactly how much this patch set helps things. For instance, a time
drift test for kvm-autotest would be perfect.
tdf is ugly and deviates from how hardware works. A compelling case is
needed to justify it.
As Jan Kiszka wrote in one of his mails may be Paul's virtual time base
can be adopted to work with KVM too. BTW how virtual time base handles
SMP guest?
I really don't know. I haven't looked to deeply at the virtual time
base. Keep in mind though, that QEMU SMP is not true SMP. All VCPUs
run in lock-step.
Regards,
Anthony Liguori
Also, it's important that this is reproducible in upstream QEMU and not
just in KVM. If we can make a compelling case for the importance of
this, we can possibly work out a compromise.
I developed and tested my patch with upstream QEMU.
--
Gleb.
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