Avi Kivity wrote:
Ingo Molnar wrote:
While the change mentions that it fixes a time warp bug, it also says
it should be rare. So clearly kvm smp tsc handing is buggy.
Ingo/Thomas, (or anybody else), do you have any insight as to what kvm
can be doing wrong to trigger this behavior?
hm. Those time warps were really small, due to the small imperfections
in the "sync up all CPUs to the same moment and do a WRMSR to clear all
their TSCs" mechanism. I.e. at most a few usec time warps. I really dont
know how that should result in udevd hanging. Can you debug udevd in any
way?
Adding debug didn't help. I'll try some sysrq keys to see what the
guest thinks is happening.
many udev children are exiting; udevd itself is sleeping:
udevd S D5DCDF24 2924 573 372 594 629 535 (NOTLB)
d5dcdf38 00000086 00000002 d5dcdf24 d5dcdf20 00000000 d5dcdefc
d6169f68
d7db7f68 d5dcdf68 00000001 d5dd7560 c13b8a90 749ae8d2 00000002
000326a1
d5dd7684 c131c700 00000003 d74f8900 892d6946 00000402 ffffffff
00000000
Call Trace:
[<c060d2c9>] do_nanosleep+0x3b/0x66
[<c0439b20>] hrtimer_nanosleep+0x50/0x106
[<c04397ee>] hrtimer_wakeup+0x0/0x18
[<c0439c1f>] sys_nanosleep+0x49/0x59
[<c0404e4c>] syscall_call+0x7/0xb
[<c0600000>] xfrm_state_find+0x49f/0x51e
So likely sleeping is screwed up somehow (though only on smp).
so the only thing that KVM might be doing incorrectly here is the
emulation of the WRMSR that clears the TSC of each vcpu?
By inspection, it is correct. Of course I may be missing something, so
I'll write a unit test for it. It should also be much slower than the
native wrmsr.
Testing shows wrmsr and rdtsc function normally.
I'll try pinning the vcpus to cpus and see if that helps.
--
error compiling committee.c: too many arguments to function
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