Re: [PATCH 0/4] RFC: support for global CPU list abbreviations
On Sun, Nov 08, 2020 at 03:21:40PM -0500, Paul Gortmaker wrote: > On 2020-11-08 1:02 p.m., Paul E. McKenney wrote: > > > Or I can carry them if you wish. My expected changes in response to > > this series are shown below, and are also what I used to test it. > > Thanks Paul - that would get linux-next exposure w/o me pestering sfr. > If nobody else has objections, having them in rcu-next would be great. Unless/until someone objects, you got it! Thanx, Paul
Re: [PATCH 0/4] RFC: support for global CPU list abbreviations
On 2020-11-08 1:02 p.m., Paul E. McKenney wrote: > Or I can carry them if you wish. My expected changes in response to > this series are shown below, and are also what I used to test it. Thanks Paul - that would get linux-next exposure w/o me pestering sfr. If nobody else has objections, having them in rcu-next would be great. Paul. --
Re: [PATCH 0/4] RFC: support for global CPU list abbreviations
On Sun, Nov 08, 2020 at 11:08:12AM -0500, Paul Gortmaker wrote: > The basic objective here was to add support for "nohz_full=8-last" and/or > "rcu_nocbs="4-last" -- essentially introduce "last" as a portable > reference evaluated at boot/runtime 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. > > Looking around before starting, I noticed RCU already had a short-form > abbreviation "all" -- but if we want to treat CPU lists in a uniform > matter, then tokens shouldn't be implemented at a subsystem level and > hence be subsystem specific; each with their own variations. > > So I moved "all" to global use - for boot args, and for cgroups. Then > I added the inverse "none" and finally, the one I wanted -- "last". > > The use of "last" isn't a standalone word like "all" or "none". It will > be a part of a complete range specification, possibly with CSV separate > ranges, and possibly specified multiple times. So I had to be a bit > more careful with string matching - and hence un-inlined the parse > function as commit #1 in this series. > > But it really is a generic support for "replace token ABC with known at > boot value XYZ" - for example, it would be trivial to extend support to > add "half" as a dynamic token to be replaced with 1/2 the core count, > even though I wouldn't suggest that has a use case like "last" does. > > I tested the string matching with a bunch of intentionally badly crafted > strings in a user-space harness, and tested bootarg use with nohz_full > and rcu_nocbs, and also the post-boot cgroup use case as per below: > >root@hackbox:/sys/fs/cgroup/cpuset# mkdir foo >root@hackbox:/sys/fs/cgroup/cpuset# cd foo >root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus > >root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-last > cpuset.cpus >root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus >10-15 >root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo all > cpuset.cpus >root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus >0-15 >root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo none > cpuset.cpus >root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus > >root@hackbox:/sys/fs/cgroup/cpuset/foo# > > This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file. > > Note that the two use cases (boot and runtime) are why you see "early" > parameter in the code - I entertained just sticking the string copy on > the stack vs. the early alloc dance, but this felt more correct/robust. > The cgroup and modular code using cpulist_parse() are runtime cases. I considered doing this when adding "all" for RCU, but was just too lazy. So you are a better man than I am! ;-) I have queued these for testing, both "all" and "last" work just fine. Given that "all" works, I hereby declare "none" to be working by inspection. Therefore, for 1, 2, and 4: Tested-by: Paul E. McKenney For 3: Reviewed-by: Paul E. McKenney Or I can carry them if you wish. My expected changes in response to this series are shown below, and are also what I used to test it. Thanx, Paul diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot b/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot index 5adc675..25a765d 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE04.boot @@ -1 +1 @@ -rcutree.rcu_fanout_leaf=4 nohz_full=1-7 +rcutree.rcu_fanout_leaf=4 nohz_full=1-last diff --git a/tools/testing/selftests/rcutorture/configs/rcu/TREE08.boot b/tools/testing/selftests/rcutorture/configs/rcu/TREE08.boot index 22478fd..94d3844 100644 --- a/tools/testing/selftests/rcutorture/configs/rcu/TREE08.boot +++ b/tools/testing/selftests/rcutorture/configs/rcu/TREE08.boot @@ -1,3 +1,3 @@ rcupdate.rcu_self_test=1 rcutree.rcu_fanout_exact=1 -rcu_nocbs=0-7 +rcu_nocbs=all
[PATCH 0/4] RFC: support for global CPU list abbreviations
The basic objective here was to add support for "nohz_full=8-last" and/or "rcu_nocbs="4-last" -- essentially introduce "last" as a portable reference evaluated at boot/runtime 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. Looking around before starting, I noticed RCU already had a short-form abbreviation "all" -- but if we want to treat CPU lists in a uniform matter, then tokens shouldn't be implemented at a subsystem level and hence be subsystem specific; each with their own variations. So I moved "all" to global use - for boot args, and for cgroups. Then I added the inverse "none" and finally, the one I wanted -- "last". The use of "last" isn't a standalone word like "all" or "none". It will be a part of a complete range specification, possibly with CSV separate ranges, and possibly specified multiple times. So I had to be a bit more careful with string matching - and hence un-inlined the parse function as commit #1 in this series. But it really is a generic support for "replace token ABC with known at boot value XYZ" - for example, it would be trivial to extend support to add "half" as a dynamic token to be replaced with 1/2 the core count, even though I wouldn't suggest that has a use case like "last" does. I tested the string matching with a bunch of intentionally badly crafted strings in a user-space harness, and tested bootarg use with nohz_full and rcu_nocbs, and also the post-boot cgroup use case as per below: root@hackbox:/sys/fs/cgroup/cpuset# mkdir foo root@hackbox:/sys/fs/cgroup/cpuset# cd foo root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo 10-last > cpuset.cpus root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus 10-15 root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo all > cpuset.cpus root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus 0-15 root@hackbox:/sys/fs/cgroup/cpuset/foo# /bin/echo none > cpuset.cpus root@hackbox:/sys/fs/cgroup/cpuset/foo# cat cpuset.cpus root@hackbox:/sys/fs/cgroup/cpuset/foo# This was on a 16 core machine with CONFIG_NR_CPUS=16 in .config file. Note that the two use cases (boot and runtime) are why you see "early" parameter in the code - I entertained just sticking the string copy on the stack vs. the early alloc dance, but this felt more correct/robust. The cgroup and modular code using cpulist_parse() are runtime cases. --- Cc: Frederic Weisbecker Cc: "Paul E. McKenney" Cc: Josh Triplett Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Li Zefan Paul Gortmaker (4): cpumask: un-inline cpulist_parse; prepare for ascii helpers cpumask: make "all" alias global and not just RCU cpumask: add a "none" alias to complement "all" cpumask: add "last" alias for cpu list specifications .../admin-guide/kernel-parameters.rst | 20 +++ .../admin-guide/kernel-parameters.txt | 4 +- include/linux/cpumask.h | 12 +- kernel/rcu/tree_plugin.h | 13 +- lib/cpumask.c | 132 ++ 5 files changed, 158 insertions(+), 23 deletions(-) -- 2.25.1
