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authorPaul E. McKenney <paulmck@linux.ibm.com>2019-03-05 15:28:19 -0800
committerPaul E. McKenney <paulmck@linux.ibm.com>2019-03-26 14:37:49 -0700
commitda8739f23fadf05809c6c37c327367b229467045 (patch)
tree665dafa91dfb5d47e077582d74f562974eea3119
parentb2eb85b49a576515fb845cb12568b173c2bedffc (diff)
rcu: Allow rcu_nocbs= to specify all CPUs
Currently, the rcu_nocbs= kernel boot parameter requires that a specific list of CPUs be specified, and has no way to say "all of them". As noted by user RavFX in a comment to Phoronix topic 1002538, this is an inconvenient side effect of the removal of the RCU_NOCB_CPU_ALL Kconfig option. This commit therefore enables the rcu_nocbs= kernel boot parameter to be given the string "all", as in "rcu_nocbs=all" to specify that all CPUs on the system are to have their RCU callbacks offloaded. Another approach would be to make cpulist_parse() check for "all", but there are uses of cpulist_parse() that do other checking, which could conflict with an "all". This commit therefore focuses on the specific use of cpulist_parse() in rcu_nocb_setup(). Just a note to other people who would like changes to Linux-kernel RCU: If you send your requests to me directly, they might get fixed somewhat faster. RavFX's comment was posted on January 22, 2018 and I first saw it on March 5, 2019. And the only reason that I found it -at- -all- was that I was looking for projects using RCU, and my search engine showed me that Phoronix comment quite by accident. Your choice, though! ;-) Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
-rw-r--r--Documentation/admin-guide/kernel-parameters.txt4
-rw-r--r--kernel/rcu/tree_plugin.h5
2 files changed, 7 insertions, 2 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90bb644..d377a2166b79 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3623,7 +3623,9 @@
see CONFIG_RAS_CEC help text.
rcu_nocbs= [KNL]
- The argument is a cpu list, as described above.
+ The argument is a cpu list, as described above,
+ except that the string "all" can be used to
+ specify every CPU on the system.
In kernels built with CONFIG_RCU_NOCB_CPU=y, set
the specified list of CPUs to be no-callback CPUs.
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index d408661d5fb7..ed4a6dabf31d 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1776,7 +1776,10 @@ static void zero_cpu_stall_ticks(struct rcu_data *rdp)
static int __init rcu_nocb_setup(char *str)
{
alloc_bootmem_cpumask_var(&rcu_nocb_mask);
- cpulist_parse(str, rcu_nocb_mask);
+ if (!strcasecmp(str, "all"))
+ cpumask_setall(rcu_nocb_mask);
+ else
+ cpulist_parse(str, rcu_nocb_mask);
return 1;
}
__setup("rcu_nocbs=", rcu_nocb_setup);