From: Marco Elver <elver@google.com>
To: elver@google.com, Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <frederic@kernel.org>,
Ingo Molnar <mingo@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Dmitry Vyukov <dvyukov@google.com>,
Michael Ellerman <mpe@ellerman.id.au>,
linuxppc-dev@lists.ozlabs.org, linux-perf-users@vger.kernel.org,
x86@kernel.org, linux-sh@vger.kernel.org,
kasan-dev@googlegroups.com, linux-kernel@vger.kernel.org
Subject: [PATCH v2 00/13] perf/hw_breakpoint: Optimize for thousands of tasks
Date: Tue, 28 Jun 2022 11:58:20 +0200 [thread overview]
Message-ID: <20220628095833.2579903-1-elver@google.com> (raw)
The hw_breakpoint subsystem's code has seen little change in over 10
years. In that time, systems with >100s of CPUs have become common,
along with improvements to the perf subsystem: using breakpoints on
thousands of concurrent tasks should be a supported usecase.
The breakpoint constraints accounting algorithm is the major bottleneck
in doing so:
1. toggle_bp_slot() and fetch_bp_busy_slots() are O(#cpus * #tasks):
Both iterate through all CPUs and call task_bp_pinned(), which is
O(#tasks).
2. Everything is serialized on a global mutex, 'nr_bp_mutex'.
The series progresses with the simpler optimizations and finishes with
the more complex optimizations:
1. We first optimize task_bp_pinned() to only take O(1) on average.
2. Rework synchronization to allow concurrency when checking and
updating breakpoint constraints for tasks.
3. Eliminate the O(#cpus) loops in the CPU-independent case.
Along the way, smaller micro-optimizations and cleanups are done as they
seemed obvious when staring at the code (but likely insignificant).
The result is (on a system with 256 CPUs) that we go from:
| $> perf bench -r 30 breakpoint thread -b 4 -p 64 -t 64
[ ^ more aggressive benchmark parameters took too long ]
| # Running 'breakpoint/thread' benchmark:
| # Created/joined 30 threads with 4 breakpoints and 64 parallelism
| Total time: 236.418 [sec]
|
| 123134.794271 usecs/op
| 7880626.833333 usecs/op/cpu
... to the following with all optimizations:
| $> perf bench -r 30 breakpoint thread -b 4 -p 64 -t 64
| Total time: 0.067 [sec]
|
| 35.292187 usecs/op
| 2258.700000 usecs/op/cpu
On the used test system, that's an effective speedup of ~3490x per op.
Which is on par with the theoretical ideal performance through
optimizations in hw_breakpoint.c (constraints accounting disabled), and
only 12% slower than no breakpoints at all.
Changelog
---------
v2:
* Add KUnit test suite.
* Remove struct bp_busy_slots and simplify functions.
* Add "powerpc/hw_breakpoint: Avoid relying on caller synchronization".
* Add "locking/percpu-rwsem: Add percpu_is_write_locked() and percpu_is_read_locked()".
* Use percpu-rwsem instead of rwlock.
* Use task_struct::perf_event_mutex instead of sharded mutex.
* Drop v1 "perf/hw_breakpoint: Optimize task_bp_pinned() if CPU-independent".
* Add "perf/hw_breakpoint: Introduce bp_slots_histogram".
* Add "perf/hw_breakpoint: Optimize max_bp_pinned_slots() for CPU-independent task targets".
* Add "perf/hw_breakpoint: Optimize toggle_bp_slot() for CPU-independent task targets".
* Apply Acked-by/Reviewed-by given in v1 for unchanged patches.
==> Speedup of ~3490x (vs. ~3315x in v1).
v1: https://lore.kernel.org/all/20220609113046.780504-1-elver@google.com/
Marco Elver (13):
perf/hw_breakpoint: Add KUnit test for constraints accounting
perf/hw_breakpoint: Clean up headers
perf/hw_breakpoint: Optimize list of per-task breakpoints
perf/hw_breakpoint: Mark data __ro_after_init
perf/hw_breakpoint: Optimize constant number of breakpoint slots
perf/hw_breakpoint: Make hw_breakpoint_weight() inlinable
perf/hw_breakpoint: Remove useless code related to flexible
breakpoints
powerpc/hw_breakpoint: Avoid relying on caller synchronization
locking/percpu-rwsem: Add percpu_is_write_locked() and
percpu_is_read_locked()
perf/hw_breakpoint: Reduce contention with large number of tasks
perf/hw_breakpoint: Introduce bp_slots_histogram
perf/hw_breakpoint: Optimize max_bp_pinned_slots() for CPU-independent
task targets
perf/hw_breakpoint: Optimize toggle_bp_slot() for CPU-independent task
targets
arch/powerpc/kernel/hw_breakpoint.c | 53 ++-
arch/sh/include/asm/hw_breakpoint.h | 5 +-
arch/x86/include/asm/hw_breakpoint.h | 5 +-
include/linux/hw_breakpoint.h | 1 -
include/linux/percpu-rwsem.h | 6 +
include/linux/perf_event.h | 3 +-
kernel/events/Makefile | 1 +
kernel/events/hw_breakpoint.c | 594 ++++++++++++++++++++-------
kernel/events/hw_breakpoint_test.c | 321 +++++++++++++++
kernel/locking/percpu-rwsem.c | 6 +
lib/Kconfig.debug | 10 +
11 files changed, 826 insertions(+), 179 deletions(-)
create mode 100644 kernel/events/hw_breakpoint_test.c
--
2.37.0.rc0.161.g10f37bed90-goog
next reply other threads:[~2022-06-28 9:59 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-28 9:58 Marco Elver [this message]
2022-06-28 9:58 ` [PATCH v2 01/13] perf/hw_breakpoint: Add KUnit test for constraints accounting Marco Elver
2022-06-28 12:53 ` Dmitry Vyukov
2022-06-28 13:26 ` Marco Elver
2022-06-28 9:58 ` [PATCH v2 02/13] perf/hw_breakpoint: Clean up headers Marco Elver
2022-06-28 9:58 ` [PATCH v2 03/13] perf/hw_breakpoint: Optimize list of per-task breakpoints Marco Elver
2022-06-28 13:08 ` Dmitry Vyukov
2022-06-28 14:53 ` Marco Elver
2022-06-28 15:27 ` Dmitry Vyukov
2022-06-28 9:58 ` [PATCH v2 04/13] perf/hw_breakpoint: Mark data __ro_after_init Marco Elver
2022-06-28 9:58 ` [PATCH v2 05/13] perf/hw_breakpoint: Optimize constant number of breakpoint slots Marco Elver
2022-06-28 9:58 ` [PATCH v2 06/13] perf/hw_breakpoint: Make hw_breakpoint_weight() inlinable Marco Elver
2022-06-28 13:16 ` Dmitry Vyukov
2022-06-28 9:58 ` [PATCH v2 07/13] perf/hw_breakpoint: Remove useless code related to flexible breakpoints Marco Elver
2022-06-28 13:18 ` Dmitry Vyukov
2022-06-28 9:58 ` [PATCH v2 08/13] powerpc/hw_breakpoint: Avoid relying on caller synchronization Marco Elver
2022-06-28 13:21 ` Dmitry Vyukov
2022-07-01 8:54 ` Christophe Leroy
2022-07-01 9:41 ` Marco Elver
2022-07-01 10:15 ` Christophe Leroy
2022-06-28 9:58 ` [PATCH v2 09/13] locking/percpu-rwsem: Add percpu_is_write_locked() and percpu_is_read_locked() Marco Elver
2022-06-28 14:44 ` Dmitry Vyukov
2022-06-28 9:58 ` [PATCH v2 10/13] perf/hw_breakpoint: Reduce contention with large number of tasks Marco Elver
2022-06-28 14:45 ` Dmitry Vyukov
2022-06-28 9:58 ` [PATCH v2 11/13] perf/hw_breakpoint: Introduce bp_slots_histogram Marco Elver
2022-06-28 14:52 ` Dmitry Vyukov
2022-06-28 9:58 ` [PATCH v2 12/13] perf/hw_breakpoint: Optimize max_bp_pinned_slots() for CPU-independent task targets Marco Elver
2022-06-28 15:41 ` Dmitry Vyukov
2022-06-28 9:58 ` [PATCH v2 13/13] perf/hw_breakpoint: Optimize toggle_bp_slot() " Marco Elver
2022-06-28 10:54 ` Marco Elver
2022-06-28 15:45 ` Dmitry Vyukov
2022-06-28 16:00 ` Marco Elver
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