From: Paul Gortmaker <paul.gortmaker@windriver.com>
To: linux-kernel@vger.kernel.org
Cc: lizefan@huawei.com, mingo@kernel.org, tglx@linutronix.de,
josh@joshtriplett.org, yury.norov@gmail.com,
peterz@infradead.org, paulmck@kernel.org, fweisbec@gmail.com,
linux@rasmusvillemoes.dk, andriy.shevchenko@linux.intel.com,
Paul Gortmaker <paul.gortmaker@windriver.com>
Subject: [PATCH v3 0/8] support for bitmap (and hence CPU) list "N" abbreviation
Date: Tue, 26 Jan 2021 12:11:33 -0500 [thread overview]
Message-ID: <20210126171141.122639-1-paul.gortmaker@windriver.com> (raw)
The basic objective here was to add support for "nohz_full=8-N" and/or
"rcu_nocbs="4-N" -- essentially introduce "N" as a portable reference
to the last core, evaluated at boot for anything using a CPU list.
The thinking behind this, is that people carve off a few early CPUs to
support housekeeping tasks, and perhaps dedicate one to a busy I/O
peripheral, and then the remaining pool of CPUs out to the end are a
part of a commonly configured pool used for the real work the user
cares about.
Extend that logic out to a fleet of machines - some new, and some
nearing EOL, and you've probably got a wide range of core counts to
contend with - even though the early number of cores dedicated to the
system overhead probably doesn't vary.
This change would enable sysadmins to have a common bootarg across all
such systems, and would also avoid any off-by-one fencepost errors that
happen for users who might briefly forget that core counts start at zero.
Originally I did this at the CPU subsys level, but Yury suggested it
be moved down further to bitmap level itself, which made the core
implementation [6/8] smaller and less complex, but the series longer.
New self tests are added to better exercise what bitmap range/region
currently supports, and new tests are added for the new "N" support.
Also tested boot arg and the post-boot cgroup use case as per below:
root@hackbox:~# cat /proc/cmdline
BOOT_IMAGE=/boot/bzImage root=/dev/sda1 rcu_nocbs=2,3,8-N:1/2
root@hackbox:~# dmesg|grep Offl
rcu: Offload RCU callbacks from CPUs: 2-3,8,10,12,14.
root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-N > cpuset.cpus
root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
10-15
root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo N-N:N/N > cpuset.cpus
root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus
15
This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file.
Note that "N" is a dynamic quantity, and can change scope if the bitmap
is changed in size. So at the risk of stating the obvious, don't use it
for "burn_eFuse=128-N" or "secure_erase_firmware=32-N" type stuff.
Paul.
---
[v1: https://lore.kernel.org/lkml/20210106004850.GA11682@paulmck-ThinkPad-P72/
[v2: push code down from cpu subsys to core bitmap code as per
Yury's comments. Change "last" to simply be "N" as per PeterZ.]
https://lore.kernel.org/lkml/20210121223355.59780-1-paul.gortmaker@windriver.com/
[v3: Allow "N" to be used anywhere in the region spec, i.e. "N-N:N/N" vs.
just being allowed at end of range like "0-N". Add new self-tests. Drop
"all" and "none" aliases as redundant and not worth the extra complication. ]
Cc: Li Zefan <lizefan@huawei.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Yury Norov <yury.norov@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
---
Paul Gortmaker (8):
lib: test_bitmap: clearly separate ERANGE from EINVAL tests.
lib: test_bitmap: add more start-end:offset/len tests
lib: bitmap: fold nbits into region struct
lib: bitmap: move ERANGE check from set_region to check_region
lib: bitmap_getnum: separate arg into region and field
lib: bitmap: support "N" as an alias for size of bitmap
lib: test_bitmap: add tests for "N" alias
rcu: deprecate "all" option to rcu_nocbs=
.../admin-guide/kernel-parameters.rst | 2 +
.../admin-guide/kernel-parameters.txt | 4 +-
kernel/rcu/tree_plugin.h | 6 +--
lib/bitmap.c | 46 ++++++++++--------
lib/test_bitmap.c | 48 ++++++++++++++++---
5 files changed, 72 insertions(+), 34 deletions(-)
--
2.17.1
next reply other threads:[~2021-01-27 0:28 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-26 17:11 Paul Gortmaker [this message]
2021-01-26 17:11 ` [PATCH 1/8] lib: test_bitmap: clearly separate ERANGE from EINVAL tests Paul Gortmaker
2021-01-26 21:04 ` Andy Shevchenko
2021-01-27 7:21 ` Paul Gortmaker
2021-01-26 17:11 ` [PATCH 2/8] lib: test_bitmap: add more start-end:offset/len tests Paul Gortmaker
2021-01-26 21:11 ` Andy Shevchenko
2021-01-27 3:03 ` Yury Norov
2021-01-26 17:11 ` [PATCH 3/8] lib: bitmap: fold nbits into region struct Paul Gortmaker
2021-01-26 21:16 ` Andy Shevchenko
2021-01-26 21:18 ` Andy Shevchenko
2021-01-27 8:02 ` Paul Gortmaker
2021-01-28 0:47 ` Yury Norov
2021-01-28 10:17 ` Andy Shevchenko
2021-01-27 3:08 ` Yury Norov
2021-01-26 17:11 ` [PATCH 4/8] lib: bitmap: move ERANGE check from set_region to check_region Paul Gortmaker
2021-01-26 21:19 ` Andy Shevchenko
2021-01-27 3:12 ` Yury Norov
2021-01-26 17:11 ` [PATCH 5/8] lib: bitmap_getnum: separate arg into region and field Paul Gortmaker
2021-01-26 21:23 ` Andy Shevchenko
2021-01-27 2:58 ` Yury Norov
2021-01-27 8:38 ` Paul Gortmaker
2021-01-26 17:11 ` [PATCH 6/8] lib: bitmap: support "N" as an alias for size of bitmap Paul Gortmaker
2021-01-26 21:37 ` Andy Shevchenko
2021-01-26 21:41 ` Andy Shevchenko
2021-01-27 17:57 ` Yury Norov
2021-01-27 8:20 ` Paul Gortmaker
2021-01-26 17:11 ` [PATCH 7/8] lib: test_bitmap: add tests for "N" alias Paul Gortmaker
2021-01-26 17:11 ` [PATCH 8/8] rcu: deprecate "all" option to rcu_nocbs= Paul Gortmaker
2021-01-26 21:36 ` Yury Norov
2021-01-26 22:17 ` Paul E. McKenney
2021-01-26 22:27 ` [PATCH v3 0/8] support for bitmap (and hence CPU) list "N" abbreviation Yury Norov
2021-01-27 9:12 ` Paul Gortmaker
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