On Wed, May 02, 2007 at 11:37:57AM -0500, Nathan Lynch wrote: > Hi Gautham- > > I believe that the powerpc behavior was established before > cpu_present_map was introduced.
Ok. I guess the same is the reason with a few other architectures like s390. > > > > I am not entirely surely if it's due cpu hotplug because > > both i386 and powerpc support it! > > powerpc also supports processor add and remove (as opposed to > online/offline); i386 does not AFAIK. I think this may be a reason > for the difference. > Well, ACPI seems to be supporting it. acpi_processor_hotadd_init() in drivers/acpi/processor_core.c appears to be equivalent to pSeries_add_processor(), except that the former creates the sysfs entries on a hot add, while the later just updates the cpu_present map. > > > When I do a > > "echo 1 > /sys/devices/system/cpu/cpuX/online" on a power box as root, > > I might get "-bash: echo: write error: Invalid argument" > > because cpuX might not be present! > > > > In case of lpar, cpu_present_map need not necessarily be equal to > > cpu_possible_map, so the above error is observable. > > Working as intended. You have to add a cpu to the partition before > you can online it. > > > > Is this discrepency intentional ? > > Or is it due to the fact that in most cases, > > cpu_present_map == cpu_possible_map, so lets not bother about it :-? > > I think it's the inevitable result when architectures are free to > invent their own versions of the same sysfs interface. But is it > really causing a problem in this case? > No, it is not causing any problems :-) I was just overwhelmed to see cpu0 to cpu77 in the sysfs entries on the lpar which I was using. Looking at the kernel code, I figured out that the MAX_CPUS for that lpar was 39 and each virtual cpu was probably running 2 threads. That explained the 78 sysfs entries. Thanks for the explaination anyway. Regards gautham. -- Gautham R Shenoy Linux Technology Center IBM India. "Freedom comes with a price tag of responsibility, which is still a bargain, because Freedom is priceless!" - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/