Messages in this thread | | | Date | Tue, 27 Oct 2020 16:07:10 -0700 | Subject | [PATCH v5 0/1] mmap_lock: add tracepoints around lock acquisition | From | Axel Rasmussen <> |
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This patchset adds tracepoints around mmap_lock acquisition. This is useful so we can measure the latency of lock acquisition, in order to detect contention.
This version is based upon linux-next (since it depends on some recently-merged patches [1] [2]).
I removed the existing {Reviewed,Acked}-by: lines from v4, since I think the patch has changed significantly enough to warrant another look (and I figure it's better to err in this direction in any case :) ).
Changes since v4:
- Redesigned buffer allocation to deal with the fact that a trace event might be interrupted by e.g. an IRQ, for which a per-cpu buffer is insufficient. Now we allocate one buffer per CPU * one buffer per context we might be called in (currently 4: normal, irq, softirq, NMI). We have three trace events which can potentially all be enabled, and all of which need a buffer; to avoid further multiplying the number of buffers by 3, they share the same set of buffers, which requires a spinlock + counter setup so we only allocate the buffers once, and then free them only when *all* of the trace events are _unreg()-ed.
Changes since v3:
- Switched EXPORT_SYMBOL to EXPORT_TRACEPOINT_SYMBOL, removed comment.
- Removed redundant trace_..._enabled() check.
- Defined the three TRACE_EVENTs separately, instead of sharing an event class. The tradeoff is 524 more bytes in .text, but the start_locking and released events no longer have a vestigial "success" field, so they're simpler + faster.
Changes since v2:
- Refactored tracing helper functions so the helpers are simper, but the locking functinos are slightly more verbose. Overall, this decreased the delta to mmap_lock.h slightly.
- Fixed a typo in a comment. :)
Changes since v1:
- Functions renamed to reserve the "trace_" prefix for actual tracepoints.
- We no longer measure the duration directly. Instead, users are expected to construct a synthetic event which computes the interval between "start locking" and "acquire returned".
- The new helper for checking if tracepoints are enabled in a header is used to avoid un-inlining any of the lock wrappers. This yields ~zero overhead if the tracepoints aren't enabled, and therefore obviates the need for a Kconfig for this change.
[1] https://lore.kernel.org/patchwork/patch/1316922/ [2] https://lore.kernel.org/patchwork/patch/1311996/
Axel Rasmussen (1): mmap_lock: add tracepoints around lock acquisition
include/linux/mmap_lock.h | 95 +++++++++++++++- include/trace/events/mmap_lock.h | 107 ++++++++++++++++++ mm/Makefile | 2 +- mm/mmap_lock.c | 187 +++++++++++++++++++++++++++++++ 4 files changed, 385 insertions(+), 6 deletions(-) create mode 100644 include/trace/events/mmap_lock.h create mode 100644 mm/mmap_lock.c
-- 2.29.0.rc2.309.g374f81d7ae-goog
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