Dor Laor wrote:
Anthony Liguori wrote:
The last time I posted the KVM patch series to qemu-devel, the -tdf
patch met with
some opposition. Since today we implement timer catch-up in the
in-kernel PIT and
the in-kernel PIT is used by default, it doesn't seem all that
valuable to have
timer catch-up in userspace too.
Removing it will reduce our divergence from QEMU.
IMHO the in kernel PIT should go away, there is no reason to keep it
except that userspace PIT drifts.
I agree fully :-) But there's certainly no reason to keep -tdf and the
in-kernel PIT. Since we're using the in-kernel PIT right now, I'd like
to get rid of -tdf.
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.
I'd still like to see some harder evidence of the benefits of tdf. For
a specific guest, with a specific configuration, how much better is the
drift with this series. The answer shouldn't be "movie's play better" :-)
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.
Regards,
Anthony Liguori
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