On 03/05/13 21:03, mdroth wrote:> On Mon, Mar 04, 2013 at 11:19:56PM +0100,
Laszlo Ersek wrote:
>> +#if defined(__linux__)
>
> There's a section in commands-posix.c set aside under "linux-specific
> implementations" for these, and another underneath for stubs so we can
> avoid having too many ifdef's.
I'll check it, thanks.
>> + buf = g_strdup_printf("/sys/devices/system/cpu/cpu%ld/online",
>> + current);
>> + f = fopen(buf, "r");
>> + if (f == NULL) {
>> + error_setg_errno(&local_err, errno, "fopen(\"%s\", \"r\")",
>> buf);
>> + } else {
>> + unsigned online;
>> +
>> + if (fscanf(f, "%u", &online) != 1) {
>
> On Fedora 18 and Ubuntu 12.04 at least there doesn't seem to be per-cpu
> values for online/offline/etc, but instead just a 'global' entry at
> /sys/devices/system/cpu/{online,offline} that provides a range. This is
> what's currently described in
> linux/Documentation/ABI/testing/sysfs-devices-system-cpu as well.
>
> Is that file also available on the distro you're testing with? Hopefully
> there's a single interfaces we can rely on.
On RHEL-6, both "/sys/devices/system/cpu/cpu*/online" and
"/sys/devices/system/cpu/online " are available.
On RHEL-5, only "/sys/devices/system/cpu/cpu*/online" is available.
"/sys/devices/system/cpu/cpu*/online" is documented in
"Documentation/cpu-hotplug.txt", in all of RHEL-5, RHEL-6, and upstream
Linux.
#pwd
#/sys/devices/system/cpu
#ls -l
total 0
drwxr-xr-x 10 root root 0 Sep 19 07:44 .
drwxr-xr-x 13 root root 0 Sep 19 07:45 ..
drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu0
drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu1
drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu2
drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu3
drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu4
drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu5
drwxr-xr-x 3 root root 0 Sep 19 07:44 cpu6
drwxr-xr-x 3 root root 0 Sep 19 07:48 cpu7
Under each directory you would find an "online" file which is the control
file to logically online/offline a processor.
Q: Does hot-add/hot-remove refer to physical add/remove of cpus?
A: The usage of hot-add/remove may not be very consistently used in the
code.
CONFIG_HOTPLUG_CPU enables logical online/offline capability in the kernel.
To support physical addition/removal, one would need some BIOS hooks and
the platform should have something like an attention button in PCI hotplug.
CONFIG_ACPI_HOTPLUG_CPU enables ACPI support for physical add/remove of
CPUs.
The kernels you mention may not have CONFIG_HOTPLUG_CPU enabled
(consequently they would probably not support the functionality either).
... I just checked "/boot/config-3.8.2-201.fc18.x86_64" in
"kernel-3.8.2-201.fc18.x86_64.rpm" and all required config options seem
to be set. I checked on a much older F18 guest as well
(3.6.10-4.fc18.x86_64), and the per-cpu "online" files are there. (Not
for cpu0, but I'll address that in response to Eric's review.) I'm not
sure why you don't get them under F18.
Thanks
Laszlo
