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authorRusty Russell <rusty@rustcorp.com.au>2009-12-17 17:43:29 (GMT)
committerRusty Russell <rusty@rustcorp.com.au>2009-12-17 01:13:29 (GMT)
commit4251417484a1775ba5cbfe38c67e6d5af9615de4 (patch)
tree9a4c6ba5406fad17b8c2715b3e1f9b68d56a81ad /Documentation/cpu-hotplug.txt
parent62ac12795095dc959649c66ace78708e7ac52477 (diff)
cpumask: don't recommend set_cpus_allowed hack in Documentation/cpu-hotplug.txt
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au> Cc: Gautham R Shenoy <ego@in.ibm.com> Cc: Ashok Raj <ashok.raj@intel.com>
Diffstat (limited to 'Documentation/cpu-hotplug.txt')
-rw-r--r--Documentation/cpu-hotplug.txt49
1 files changed, 17 insertions, 32 deletions
diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index 4d4a644b..a99d703 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -315,41 +315,26 @@ A: The following are what is required for CPU hotplug infrastructure to work
Q: I need to ensure that a particular cpu is not removed when there is some
work specific to this cpu is in progress.
-A: First switch the current thread context to preferred cpu
+A: There are two ways. If your code can be run in interrupt context, use
+ smp_call_function_single(), otherwise use work_on_cpu(). Note that
+ work_on_cpu() is slow, and can fail due to out of memory:
int my_func_on_cpu(int cpu)
{
- cpumask_t saved_mask, new_mask = CPU_MASK_NONE;
- int curr_cpu, err = 0;
-
- saved_mask = current->cpus_allowed;
- cpu_set(cpu, new_mask);
- err = set_cpus_allowed(current, new_mask);
-
- if (err)
- return err;
-
- /*
- * If we got scheduled out just after the return from
- * set_cpus_allowed() before running the work, this ensures
- * we stay locked.
- */
- curr_cpu = get_cpu();
-
- if (curr_cpu != cpu) {
- err = -EAGAIN;
- goto ret;
- } else {
- /*
- * Do work : But cant sleep, since get_cpu() disables preempt
- */
- }
- ret:
- put_cpu();
- set_cpus_allowed(current, saved_mask);
- return err;
- }
-
+ int err;
+ get_online_cpus();
+ if (!cpu_online(cpu))
+ err = -EINVAL;
+ else
+#if NEEDS_BLOCKING
+ err = work_on_cpu(cpu, __my_func_on_cpu, NULL);
+#else
+ smp_call_function_single(cpu, __my_func_on_cpu, &err,
+ true);
+#endif
+ put_online_cpus();
+ return err;
+ }
Q: How do we determine how many CPUs are available for hotplug.
A: There is no clear spec defined way from ACPI that can give us that

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