On Sun, Feb 21, 2021 at 03:08:19AM -0500, Paul Gortmaker wrote: > This is the 5th and final version of this series. We got some good > improvements, like adding self-tests, using "N" as "just another number" > that could be used anywhere, and making things not CPU specific. > > But now it is time to close this review out since is down to just > hand-wringing over hypothetical use cases, bikeshedding on upper/lower > case, and a wild goose chase on trying to avoid adding a function arg. > > So, once again - thanks to all who provided input; it was all considered > even if not all of it was used. And in that vein, just to be clear: > > 1) There will be no adaptive modifying or guessing what the user meant if > a range turns out to be invalid. The caller will be responsible for > handling the -EINVAL just as things are currently today. > > 2) There will be no use of "L" or lower case "n" because there is simply > no need for it. Yes, it would be simple enough to add, but it complicates > things and would also be impossible to remove later, once it went mainline. > > > The original text from v4 follows: > > 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 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. > ---
Acked-by: Yury Norov <yury.no...@gmail.com> > [v5: go back to v3 location of "nbits" in region. Add acks/reviewed.] > > [v4: pair nbits with region, instead of inside it. Split EINVAL and > ERANGE tests. Don't handle start/end/offset within a macro to > abstract away nbits usage. Added some Reviwed-by/Ack tags.] > > https://lore.kernel.org/lkml/20210209225907.78405-1-paul.gortma...@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. ] > > https://lore.kernel.org/lkml/20210126171141.122639-1-paul.gortma...@windriver.com/ > > [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.gortma...@windriver.com/ > > [v1: https://lore.kernel.org/lkml/20210106004850.GA11682@paulmck-ThinkPad-P72/ > > Cc: Li Zefan <lize...@huawei.com> > Cc: Ingo Molnar <mi...@kernel.org> > Cc: Yury Norov <yury.no...@gmail.com> > Cc: Thomas Gleixner <t...@linutronix.de> > Cc: Josh Triplett <j...@joshtriplett.org> > Cc: Peter Zijlstra <pet...@infradead.org> > Cc: "Paul E. McKenney" <paul...@kernel.org> > Cc: Frederic Weisbecker <fweis...@gmail.com> > Cc: Rasmus Villemoes <li...@rasmusvillemoes.dk> > Cc: Andy Shevchenko <andriy.shevche...@linux.intel.com> > > > > Paul Gortmaker (8): > lib: test_bitmap: clearly separate ERANGE from EINVAL tests. > lib: test_bitmap: add tests to trigger ERANGE case. > 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: 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 | 7 +++ > .../admin-guide/kernel-parameters.txt | 4 +- > kernel/rcu/tree_plugin.h | 6 +-- > lib/bitmap.c | 49 +++++++++++-------- > lib/test_bitmap.c | 46 ++++++++++++++--- > 5 files changed, 79 insertions(+), 33 deletions(-) > > -- > 2.30.0
