From: Peter Oskolkov <posk@posk.io>
To: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Darren Hart <dvhart@infradead.org>,
Vincent Guittot <vincent.guittot@linaro.org>
Cc: Peter Oskolkov <posk@google.com>,
Andrei Vagin <avagin@google.com>, Paul Turner <pjt@google.com>,
Ben Segall <bsegall@google.com>, Aaron Lu <aaron.lwe@gmail.com>
Subject: [PATCH for 5.9 0/3] FUTEX_SWAP (tip/locking/core)
Date: Wed, 22 Jul 2020 16:45:35 -0700 [thread overview]
Message-ID: <20200722234538.166697-1-posk@posk.io> (raw)
From: Peter Oskolkov <posk@google.com>
As Paul Turner presented at LPC in 2013 ...
- pdf: http://pdxplumbers.osuosl.org/2013/ocw//system/presentations/1653/original/LPC%20-%20User%20Threading.pdf
- video: https://www.youtube.com/watch?v=KXuZi9aeGTw
... Google has developed an M:N userspace threading subsystem backed
by Google-private SwitchTo Linux Kernel API (page 17 in the pdf referenced
above). This subsystem provides latency-sensitive services at Google with
fine-grained user-space control/scheduling over what is running when,
and this subsystem is used widely internally (called schedulers or fibers).
This patchset is the first step to open-source this work. As explained
in the linked pdf and video, SwitchTo API has three core operations: wait,
resume, and swap (=switch). So this patchset adds a FUTEX_SWAP operation
that, in addition to FUTEX_WAIT and FUTEX_WAKE, will provide a foundation
on top of which user-space threading libraries can be built.
Another common use case for FUTEX_SWAP is message passing a-la RPC
between tasks: task/thread T1 prepares a message,
wakes T2 to work on it, and waits for the results; when T2 is done, it
wakes T1 and waits for more work to arrive. Currently the simplest
way to implement this is
a. T1: futex-wake T2, futex-wait
b. T2: wakes, does what it has been woken to do
c. T2: futex-wake T1, futex-wait
With FUTEX_SWAP, steps a and c above can be reduced to one futex operation
that runs 5-10 times faster.
Patches in this patchset:
Patch 1: introduce FUTEX_SWAP futex operation that,
internally, does wake + wait. The purpose of this patch is
to work out the API.
Patch 2: a first rough attempt to make FUTEX_SWAP faster than
what wake + wait can do.
Patch 3: a selftest that can also be used to benchmark FUTEX_SWAP vs
FUTEX_WAKE + FUTEX_WAIT.
Peter Oskolkov (3):
futex: introduce FUTEX_SWAP operation
futex/sched: add wake_up_process_prefer_current_cpu, use in FUTEX_SWAP
selftests/futex: add futex_swap selftest
include/linux/sched.h | 1 +
include/uapi/linux/futex.h | 2 +
kernel/futex.c | 89 ++++++--
kernel/sched/core.c | 5 +
kernel/sched/fair.c | 3 +
kernel/sched/sched.h | 1 +
.../selftests/futex/functional/.gitignore | 1 +
.../selftests/futex/functional/Makefile | 1 +
.../selftests/futex/functional/futex_swap.c | 209 ++++++++++++++++++
.../selftests/futex/include/futextest.h | 19 ++
10 files changed, 315 insertions(+), 16 deletions(-)
create mode 100644 tools/testing/selftests/futex/functional/futex_swap.c
--
2.25.1
next reply other threads:[~2020-07-22 23:45 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-22 23:45 Peter Oskolkov [this message]
2020-07-22 23:45 ` [PATCH for 5.9 1/3] futex: introduce FUTEX_SWAP operation Peter Oskolkov
2020-07-23 11:27 ` Peter Zijlstra
2020-07-24 0:25 ` Peter Oskolkov
2020-07-24 3:00 ` Waiman Long
2020-07-24 3:22 ` Peter Oskolkov
2020-07-27 9:51 ` peterz
2020-07-28 0:01 ` Peter Oskolkov
2020-07-22 23:45 ` [PATCH for 5.9 2/3] futex/sched: add wake_up_process_prefer_current_cpu, use in FUTEX_SWAP Peter Oskolkov
2020-07-22 23:45 ` [PATCH for 5.9 3/3] selftests/futex: add futex_swap selftest Peter Oskolkov
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