On 6/13/13 7:04 PM, Cody P Schafer wrote:
Hi all, I'm trying to use perf kvm to profile linux early boot.
However, perf kvm top always appears to behave as though it's in
non-callgraph mode.
During event collection perf kernel side does not walk the guest
callchain. I believe it only collects IP.
David
I dug through the code a bit, and it looks as though
machine__resolve_challchain_sample() is getting called with an
ip_callchain consistently containing only 2 entries:
PERF_CONTEXT_KERNEL followed by PERF_CONTEXT_USER. This makes it
appear that the perf_sample is not getting any callchain info from the
kernel.
System setup:
I'm running qemu as follows:
$ qemu-system-x86_64 -M pc -kernel ./bzImage -drive
file=./rootfs.ext2,if=virtio -append "root=/dev/vda console=ttyS0
earlyprintk=ttyS0 debug numa=fake=2 kmemleak=on extra_nr_node_ids=100"
-smp 8 -nographic -enable-kvm -s -m 64G
And perf kvm top as follows:
$ sudo ./perf kvm --guestvmlinux ~/vmlinux top --call-graph
The host `uname -a` is
Linux pizza 3.7.10-gentoo-r1 #1 SMP Thu Apr 25 15:11:18 PDT 2013
x86_64 Intel(R) Core(TM) i7-2720QM CPU @ 2.20GHz GenuineIntel
GNU/Linux
(And I've gotten the same results with 3.8.0-22-generic #33~precise1-Ubuntu).
The guest kernel is v3.10-rc5 with some additional patches mostly to mm/*
The version of the perf tool is 3.9.rc8.g25e33e (the version in
linus's tree today).
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