cpumask: don't recommend set_cpus_allowed hack in Documentation/cpu-hotplug.txt
PATCH 14/14 cpumask: don't recommend set_cpus_allowed hack in Documentation/cpu-hotplug.txt
Signed-off-by Rusty Russell <[email protected]>
Cc Gautham R Shenoy <[email protected]>
Cc Ashok Raj <[email protected]>
--- Documentation/cpu-hotplug.txt | 49 ++++++++++++++---------------------------- 1 file changed, 17 insertions(+), 32 deletions(-)
Documentation/cpu-hotplug.txt +17 -32
@@ -309,41 +309,26 @@ A: The following are what is required fo 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() 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; + cpu_hotplug_lock(); + 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 + cpu_hotplug_unlock(); + 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
Hi Rusty,
Quoted 13 lines · Rusty Russell
Signed-off-by Rusty Russell <[email protected]>Cc Gautham R Shenoy <[email protected]>Cc Ashok Raj <[email protected]>--- Documentation/cpu-hotplug.txt | 49 ++++++++++++++---------------------------- 1 file changed, 17 insertions(+), 32 deletions(-)Documentation/cpu-hotplug.txt +0
-0@@ -309,41 +309,26 @@ A: The following are what is required fo Q: I need to ensure that a particular cpu is not removed when there is some
Documentation/cpu-hotplug.txt A: The following are what is required fo · line 319
Quoted 10 lines
Documentation/cpu-hotplug.txt +5
-1work 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() can fail due to out of memory: int my_func_on_cpu(int cpu) { + int err; + cpu_hotplug_lock();
^^^^^^^^^^^^^^^^^^^
This needs to be get_online_cpus();
Documentation/cpu-hotplug.txt A: The following are what is required fo · line 329
Quoted 10 lines
Documentation/cpu-hotplug.txt +10
-0+ 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 + cpu_hotplug_unlock();
^^^^^^^^^^^^^^^^^^^^^
And this one should be put_online_cpus();
Quoted 5 lines
Documentation/cpu-hotplug.txt +2
-0+ 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
Signature · 2 lines
Thanks and Regards gautham
Quoted 3 lines · Gautham R Shenoy
Hi Rusty,
On Tue, Nov 03, 2009 at 02:59:06PM +1030, Rusty Russell wrote:
...
Quoted 4 lines
Documentation/cpu-hotplug.txt A: The following are what is required fo · line 319
Quoted 2 lines
Documentation/cpu-hotplug.txt +2
-0+ int err; + cpu_hotplug_lock();^^^^^^^^^^^^^^^^^^^This needs to be
get_online_cpus();
Thanks, both fixed!
Rusty.