From: Paul Gortmaker <email@example.com> To: firstname.lastname@example.org Cc: email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, email@example.com, firstname.lastname@example.org, Paul Gortmaker <email@example.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: <firstname.lastname@example.org> (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://email@example.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 <firstname.lastname@example.org> Cc: Ingo Molnar <email@example.com> Cc: Yury Norov <firstname.lastname@example.org> Cc: Thomas Gleixner <email@example.com> Cc: Josh Triplett <firstname.lastname@example.org> Cc: Peter Zijlstra <email@example.com> Cc: "Paul E. McKenney" <firstname.lastname@example.org> Cc: Frederic Weisbecker <email@example.com> Cc: Rasmus Villemoes <firstname.lastname@example.org> Cc: Andy Shevchenko <email@example.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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