Messages in this thread | | | From | Alexander Shishkin <> | Subject | [PATCH v1 0/6] perf: Add AUX data sampling | Date | Tue, 12 Jun 2018 10:51:11 +0300 |
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Hi,
This series introduces AUX data sampling for perf events, which in case of our instruction/branch tracing PMUs like Intel PT, BTS, CS ETM means execution flow history leading up to a perf event's overflow.
In case of Intel PT, this can be used as an alternative to LBR, with virtually as many as you like branches per sample. It doesn't support some of the LBR features (branch prediction indication, basic block level timing, etc [1]) and it can't be exposed as BRANCH_STACK, because that would require decoding PT stream in kernel space, which is not practical. Instead, we deliver the PT data to userspace as is, for offline processing. The PT decoder already supports presenting PT as virtual LBR.
AUX sampling is different from the snapshot mode in that it doesn't require instrumentation (for when to take a snapshot) and is better for generic data collection, when you don't yet know what you are looking for. It's also useful for automated data collection, for example, for feedback-driven compiler optimizaitions.
It's also different from the "full trace mode" in that it produces much less data and, consequently, takes up less I/O bandwidth and storage space, and takes less time to decode.
The bulk of code is in 4/6, which adds the user interface bits and adds code to measure and copy out AUX data. 1/6 and 2/6 close the races around the sampling code, 3/6 is a helper, 5/6 kills the PERF_FLAG_FD_OUTPUT which has been effectively dead for about 8 years now and 6/6 allows SET_OUTPUT between SW and HW contexts, which allows the tool to not carry around additional file descriptors when sampling a hardware event.
I'm not including the tooling patches, which Adrian will post separately. Meanwhile, they can be found here [2].
Changes since the last time I posted patches to this effect [3]: - instead of creating kernel events with AUX data, have the user create them and pass on to the events that they wish to see AUX samples on; - as a result, dropped most of the code.
[1] https://marc.info/?l=linux-kernel&m=147467007714928&w=2 [2] https://git.kernel.org/cgit/linux/kernel/git/ash/linux.git/log/?h=perf-aux-sampling [3] https://marc.info/?l=linux-kernel&m=147463007105836
Adrian Hunter (1): perf: Allow set-output for task contexts of different types
Alexander Shishkin (5): perf: Disable PMU around address filter adjustment perf: Disable IRQs in address filter sync path perf: Add an iterator for AUX data perf: Allow using AUX data in perf samples perf: Drop PERF_FLAG_FD_OUTPUT
include/linux/perf_event.h | 10 ++ include/uapi/linux/perf_event.h | 8 +- kernel/events/core.c | 206 +++++++++++++++++++++++++++++--- kernel/events/internal.h | 5 + kernel/events/ring_buffer.c | 34 ++++++ 5 files changed, 247 insertions(+), 16 deletions(-)
-- 2.17.1
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