On Thu, 2021-05-06 at 17:14 -0400, Steven Rostedt wrote:
> Searching for the qemu task to find what task the CID is for is not a
> reliable method, as the qemu executable may be called different names
> on
> different systems, and qemu may not even be used.
>
> Instead, trace the sched_waking and kvm_exit events and do a vsock
> connection to the CID. By doing so, you can find the task that runs the
> guest.
>
> trace-cmd wakes up "vhost-<pid>"
> vhost-<pid> wakes up "CPUX/KVM"
> CPUX/KVM calls "kvm_exit"
>
This may very well be me, but I don't get why we need to follow the
wakeup chains.
Doesn't a VMExit always happen in the thread that runs the vCPU anyway?
I mean, just by tracing 'kvm:kvm_exit', I get:
<...>-74350 [003] 903542.374465: kvm_exit: reason MSR_WRITE rip 0xffffffffac4757d4 info 0 0
<...>-74355 [012] 903542.374465: kvm_exit: reason MSR_WRITE rip 0xffffffffac4757d4 info 0 0
<...>-74350 [003] 903542.374470: kvm_exit: reason MSR_WRITE rip 0xffffffffac4757d4 info 0 0
<...>-74355 [012] 903542.374470: kvm_exit: reason MSR_WRITE rip 0xffffffffac4757d4 info 0 0
<...>-74355 [012] 903542.374485: kvm_exit: reason MSR_WRITE rip 0xffffffffac4757d4 info 0 0
<...>-74355 [012] 903542.374487: kvm_exit: reason HLT rip 0xffffffffacca465d info 0 0
<...>-74350 [003] 903542.374488: kvm_exit: reason MSR_WRITE rip 0xffffffffac4757d4 info 0 0
<...>-74350 [003] 903542.374490: kvm_exit: reason HLT rip 0xffffffffacca465d info 0 0
<...>-74341 [126] 903542.374813: kvm_exit: reason MSR_WRITE rip 0xffffffffac4757d4 info 0 0
This tells us already that 74341, 74350 and 74355 are the pids of some
vcpu threads on the host.
At this point, /proc will tell us that these are in fact vcpus of the
same VM, and which is the PID of the thread group leader that we want
to use in /sys/kernel/debug/kvm:
grep Tgid /proc/{74341,74350,74355}/status
/proc/74341/status:Tgid: 74306
/proc/74350/status:Tgid: 74306
/proc/74355/status:Tgid: 74306
ls /sys/kernel/debug/kvm/
74306-19
What am I missing?
Regards
--
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
-------------------------------------------------------------------
<<This happens because _I_ choose it to happen!>> (Raistlin Majere)
Attachment:
signature.asc
Description: This is a digitally signed message part
|