Messages in this thread Patch in this message | | | Date | Fri, 01 Jun 2012 09:40:30 -0600 | From | David Ahern <> | Subject | Re: perf kvm segfaults while reporting events |
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On 6/1/12 7:56 AM, Pradeep Kumar Surisetty wrote: > Hello > > perf kvm generats segfaults while reporting events. > > host& guest: 3.4.0-rc4 > > 1) Copied kallsyms, modules from guest to host. > > 2) recorded events on host and guest& report it using below commands. > > > [root@host]# ./perf kvm --host --guest --guestkallsyms=/tmp/guest-kallsyms --guestmodules=/tmp/guest-modules record -a -o perf.data > ^C[ perf record: Woken up 1 times to write data ] > [ perf record: Captured and wrote 0.381 MB perf.data (~16659 samples) ] > > [root@host]# ./perf kvm --host --guest --guestkallsyms=/tmp/guest-kallsyms --guestmodules=/tmp/guest-modules report -i perf.data --force > perf: Segmentation fault
The short of it is that perf-kvm needs some work.
More specifically, the guest 'machine' is not created on the report path for the above arguments. This will prevent the segfault:
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c index 93d355d..c8e1323 100644 --- a/tools/perf/util/session.c +++ b/tools/perf/util/session.c @@ -918,6 +918,8 @@ static int perf_session_deliver_event(struct perf_session *session, } return tool->sample(tool, event, sample, evsel, machine); case PERF_RECORD_MMAP: + if (machine == NULL) + return 0; return tool->mmap(tool, event, sample, machine); case PERF_RECORD_COMM: return tool->comm(tool, event, sample, machine);
The --guestmount option (which has its own problems) combined with specific pid is more stable . e.g.,
mkdir /tmp/guestmount/<vm-pid> sshfs root@<vm-ip>:/ /tmp/guestmount/<vm-pid> -o direct_io
perf kvm --host --guest --guestmount=/tmp/guestmount \ record -p <vm-pid> -o /tmp/perf.data -- sleep 1
perf kvm --host --guest --guestmount=/tmp/guestmount report -i /tmp/perf.data --force --stdio
If you use the -a argument on record with multiple VMs running without an entry in /tmp/guestmount you'll see:
Warning: 7 unprocessable samples recorded. Do you have a KVM guest running and not using 'perf kvm'?
David
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