Avi Kivity wrote:
Anders wrote:
According to powertop, I had about 15 kvm wakeups/sec with my
previous setup (nohz, no display). Now I upgraded to kvm-70 and the
timer interrupt has reappeared so I have this:
Top causes for wakeups:
25,4% (112,4) <kernel IPI> : function call interrupts
22,6% (100,0) qemu-system-x86 : kvm_arch_vcpu_ioctl_run
(pit_timer_fn)
22,6% (100,0) qemu-system-x86 : __kvm_migrate_timers (apic_timer_fn)
8,7% ( 38,5) qemu-system-x86 : sys_timer_settime (posix_timer_fn)
What could be the cause for this change? The previous kvm was from
Ubuntu 8.04, there are no changes in the guest.
Likely, the in-kernel pit. Try -no-kvm-pit.
The -no-kvm-pit did change things. However, there is still a periodic tick:
Top causes for wakeups:
34,7% (102,0) qemu-system-x86 : sys_timer_settime (posix_timer_fn)
34,0% (100,0) qemu-system-x86 : __kvm_migrate_timers (apic_timer_fn)
13,8% ( 40,7) <kernel IPI> : function call interrupts
For comparison, this is my normal output. This is with the same kernel
modules, but the userspace from Ubuntu 8.04:
Top causes for wakeups:
50,2% ( 66,0) <kernel IPI> : function call interrupts
11,3% ( 14,9) kvm : apic_mmio_write (apic_timer_fn)
In general, what are the best host/guest settings for a low number of
wakeups?
dyntick on both.
Sure. I guess my question was how to achieve that. Things like the
-no-kvm-pit advice. Also, I have used "clocksource=tsc acpi=force" on
the guest to get it to dyntick. But that seems to no longer work. So I
was wondering whether there was some known configuration that was
supposed to work.
Anders.
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