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Message-ID: <20260125200759.57816-1-hrishikesh123s@gmail.com>
Date: Sun, 25 Jan 2026 21:06:52 +0100
From: Hrishikesh Suresh <hrishikesh123s@...il.com>
To: Peter Zijlstra <peterz@...radead.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Namhyung Kim <namhyung@...nel.org>
Cc: Hrishikesh Suresh <hrishikesh123s@...il.com>,
Ingo Molnar <mingo@...hat.com>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...nel.org>,
Ian Rogers <irogers@...gle.com>,
Adrian Hunter <adrian.hunter@...el.com>,
James Clark <james.clark@...aro.org>,
Chun-Tse Shao <ctshao@...gle.com>,
Blake Jones <blakejones@...gle.com>,
Dmitry Vyukov <dvyukov@...gle.com>,
Leo Yan <leo.yan@....com>,
linux-perf-users@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: [PATCH] perf session: print all machines in session dump
perf_session__fprintf() prints only host. This has been changed to print
details of host and all guests, by traversing through the RB-Tree. These
are visible when using high verbosity (-vvvv) in KVM environments, during
perf report dumps.
Testing -
- Test 1: Record the local machine and guest VM using 'perf kvm record' and
generate the report using 'perf kvm report -vvvv -D'. The dump should show
the threads and other details related to local and guest machine.
- 1 Ubuntu VM running on Fedora host
- VM is running a noisy program =>
$ dd if=/dev/urandom of=/dev/null
- On host run =>
$ sudo ./perf kvm --guestvmlinux=/tmp/shared/guest_vmlinux \
--guestkallsyms=/tmp/shared/guest_kallsyms \
--guestmodules=/tmp/shared/guest_modules \
record -a -g -o perf.data.guest
and exit after a few seconds.
[ perf record: Woken up 9 times to write data ]
[ perf record: Captured and wrote 3.150 MB perf.data.guest \
(29311 samples) ]
- Generate dump =>
$ sudo ./perf kvm --guestkallsyms /tmp/shared/guest_kallsyms \
report -vvvv -D -i perf.data.guest > output.txt
- Check for threads associated with guest machine.
$ grep "Thread 0" output.txt
Thread 0 swapper
Thread 0 [guest/0]
PASS
- Test 2: Record the local machine and guest VM using 'perf kvm record' and
generate the report using 'perf kvm report'. The functions running on
guest VM should be seen in the report.
- Same setup as Test 1 but the test looks at the performance profile,
to check if the function names are visible.
- Peek into profile using =>
$ sudo ./perf kvm --guestkallsyms /tmp/shared/guest_kallsyms \
report -i perf.data.guest
- Samples: 29K of event 'cycles', Event count (approx.): 28711693142
Children Self Command Shared Object Symbol
35.69% 35.69% :5820 [guest.kernel.kallsyms] [g] chacha_permute
11.56% 11.56% :5820 [guest.kernel.kallsyms] [g] entry_SYSRETQ_unsXXX
11.12% 11.12% :5820 [guest.kernel.kallsyms] [g] syscall_return_viXXX
7.36% 7.36% :5820 [guest.kernel.kallsyms] [g] entry_SYSCALL_64_XXX
6.07% 6.07% :5820 [guest.kernel.kallsyms] [g] chacha_block_generic
5.40% 5.40% :5820 [guest.kernel.kallsyms] [g] _copy_to_iter
....
PASS
- Test 3: Record the local and 2 guest VMs using 'perf kvm record' and
generate the report using 'perf kvm report -vvvv -D'. The dump should show
the threads and other details related to local and guest machines.
- 1 Ubuntu and 1 Alpine VMs running on Fedora host.
- Find PIDs of qemu instances and use them during record and report
$ pgrep qemu
5816
25098
- Record the activity =>
$ sudo ./perf kvm record -p 5816,25098 -a -g -o perf.data.guests
Warning:
PID/TID switch overriding SYSTEM
[ perf record: Woken up 325927 times to write data ]
[ perf record: Captured and wrote 3.692 MB perf.data.guests \
(57389 samples) ]
- Generate dump =>
$ sudo ./perf kvm report -vvvv -D -i perf.data.guests > output.txt
- Check if the threads related to the local machine and guest VMs
are present =>
$ grep "Thread 0" output.txt
Thread 0 swapper
Thread 0 [guest/0]
NOTE: Threads from Ubuntu and Alpine VMs are bundled together and
appear as one guest machine.
Looking into output.txt =>
Threads: 6
Thread 0 [guest/0]
Thread 5816 :5816
Thread 25098 :25098
Thread 5819 :5819
Thread 5820 :5820
Thread 25103 :25103
To conclude, information is collected for both VMs and not listed
as two different guest machines.
PASS
- Test 4: Check if any guest-related information is printed in
perf annotate. This test is included because the command calls
perf_session__fprintf() in its code path when using -vvvv option.
This could be explained by inability / lack of options for 'perf annotate'
to look into guest VM from host machine, due to no option to specify the
guest's kallsyms or modules. A similar explanation for 'perf mem' could
be used, as perf_session__fprintf() is also present in its code path.
- Run annotate =>
$ sudo ./perf annotate -i perf.data.guest -vvvv > output.txt
- Check for threads from local machine or guest VM =>
$ grep "Thread 0" output.txt
Thread 0 swapper
Threads from local machine are found while threads from guest VM
are not found. It is possibly because of a lack of a guest kallsyms
option for DSO matching in perf annotate.
PASS
- Test 5: Run kvm test available on perf path
- $ sudo ./perf test kvm
89: perf kvm tests : Ok
PASS
Signed-off-by: Hrishikesh Suresh <hrishikesh123s@...il.com>
---
tools/perf/util/session.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 4236503c8f6c..6c6dfeb4eb33 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -2674,11 +2674,15 @@ size_t perf_session__fprintf_nr_events(struct perf_session *session, FILE *fp)
size_t perf_session__fprintf(struct perf_session *session, FILE *fp)
{
- /*
- * FIXME: Here we have to actually print all the machines in this
- * session, not just the host...
- */
- return machine__fprintf(&session->machines.host, fp);
+ struct rb_node *nd;
+ struct machine *pos;
+ size_t ret = machine__fprintf(&session->machines.host, fp);
+
+ for (nd = rb_first_cached(&session->machines.guests); nd; nd = rb_next(nd)) {
+ pos = rb_entry(nd, struct machine, rb_node);
+ ret += machine__fprintf(pos, fp);
+ }
+ return ret;
}
void perf_session__dump_kmaps(struct perf_session *session)
--
2.52.0
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