diff options
| author | Peter Zijlstra <peterz@infradead.org> | 2025-10-23 15:17:05 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2025-10-29 10:29:58 +0100 |
| commit | c69993ecdd4dfde2b7da08b022052a33b203da07 (patch) | |
| tree | d6b6be644f0f309d33c6b628ada969d23bd7ffc1 /tools | |
| parent | ae25884ad749e7f6e0c3565513bdc8aa2554a425 (diff) | |
perf: Support deferred user unwind
Add support for deferred userspace unwind to perf.
Where perf currently relies on in-place stack unwinding; from NMI
context and all that. This moves the userspace part of the unwind to
right before the return-to-userspace.
This has two distinct benefits, the biggest is that it moves the
unwind to a faultable context. It becomes possible to fault in debug
info (.eh_frame, SFrame etc.) that might not otherwise be readily
available. And secondly, it de-duplicates the user callchain where
multiple samples happen during the same kernel entry.
To facilitate this the perf interface is extended with a new record
type:
PERF_RECORD_CALLCHAIN_DEFERRED
and two new attribute flags:
perf_event_attr::defer_callchain - to request the user unwind be deferred
perf_event_attr::defer_output - to request PERF_RECORD_CALLCHAIN_DEFERRED records
The existing PERF_RECORD_SAMPLE callchain section gets a new
context type:
PERF_CONTEXT_USER_DEFERRED
After which will come a single entry, denoting the 'cookie' of the
deferred callchain that should be attached here, matching the 'cookie'
field of the above mentioned PERF_RECORD_CALLCHAIN_DEFERRED.
The 'defer_callchain' flag is expected on all events with
PERF_SAMPLE_CALLCHAIN. The 'defer_output' flag is expect on the event
responsible for collecting side-band events (like mmap, comm etc.).
Setting 'defer_output' on multiple events will get you duplicated
PERF_RECORD_CALLCHAIN_DEFERRED records.
Based on earlier patches by Josh and Steven.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/20251023150002.GR4067720@noisy.programming.kicks-ass.net
Diffstat (limited to 'tools')
| -rw-r--r-- | tools/include/uapi/linux/perf_event.h | 21 |
1 files changed, 20 insertions, 1 deletions
diff --git a/tools/include/uapi/linux/perf_event.h b/tools/include/uapi/linux/perf_event.h index 78a362b80027..d292f96bc06f 100644 --- a/tools/include/uapi/linux/perf_event.h +++ b/tools/include/uapi/linux/perf_event.h @@ -463,7 +463,9 @@ struct perf_event_attr { inherit_thread : 1, /* children only inherit if cloned with CLONE_THREAD */ remove_on_exec : 1, /* event is removed from task on exec */ sigtrap : 1, /* send synchronous SIGTRAP on event */ - __reserved_1 : 26; + defer_callchain: 1, /* request PERF_RECORD_CALLCHAIN_DEFERRED records */ + defer_output : 1, /* output PERF_RECORD_CALLCHAIN_DEFERRED records */ + __reserved_1 : 24; union { __u32 wakeup_events; /* wake up every n events */ @@ -1239,6 +1241,22 @@ enum perf_event_type { */ PERF_RECORD_AUX_OUTPUT_HW_ID = 21, + /* + * This user callchain capture was deferred until shortly before + * returning to user space. Previous samples would have kernel + * callchains only and they need to be stitched with this to make full + * callchains. + * + * struct { + * struct perf_event_header header; + * u64 cookie; + * u64 nr; + * u64 ips[nr]; + * struct sample_id sample_id; + * }; + */ + PERF_RECORD_CALLCHAIN_DEFERRED = 22, + PERF_RECORD_MAX, /* non-ABI */ }; @@ -1269,6 +1287,7 @@ enum perf_callchain_context { PERF_CONTEXT_HV = (__u64)-32, PERF_CONTEXT_KERNEL = (__u64)-128, PERF_CONTEXT_USER = (__u64)-512, + PERF_CONTEXT_USER_DEFERRED = (__u64)-640, PERF_CONTEXT_GUEST = (__u64)-2048, PERF_CONTEXT_GUEST_KERNEL = (__u64)-2176, |