On 06/07/2010 09:54 PM, David S. Ahern wrote:
So it's important to know how often your RHEL3/4 guest queries the PIT
(not just receives interrupts, actually reads the counter) under a
realistic load. If you have such a number (in reads/sec) that would be
a good input to this discussion.
Aps that invoke gettimeofday a lot.
Ask a stupid question, get an "it depends on the workload" answer.
As I recall RHEL3 uses the TSC
between timer interrupts, but RHEL4 samples counters on each
gettimeofday call:
http://www.mail-archive.com/kvm@xxxxxxxxxxxxxxx/msg07231.html
Because of that performance of applications that timestamp log entries
(like a certain product I work on) takes a hit on KVM unless the TSC is
the clock source.
So it looks like dropping the PIT out of the kernel, let alone the
PIC/IOAPIC, is out of the question.
--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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