Tony, On Wed, Sep 20, 2006 at 01:29:35PM -0700, Luck, Tony wrote: > On Wed, Sep 20, 2006 at 09:23:25PM +0100, Christoph Hellwig wrote: > > On Wed, Sep 20, 2006 at 12:53:47PM -0700, Stephane Eranian wrote: > > > Hello Tony, > > > > > > For Montecito PMU support, I need to determine, in a kernel module, whether > > > or not threads are enabled. The only reliable way of doing this is to > > > compute the bit-weight of cpu_sibling_map[]. This symbol is exported on > > > x86 systems, but not on IA-64 so far. This patch exports the symbol. > > > > Exporting global variables is a very bad thing, and we only do it if we > > can't avoid it at all. In this case it could be easily avoided by > > exporting a nr_siblings_per_cpu() helper. > > I also have my doubts about this in terms of hotplug cpu ... what > do you do if not all of the cpus have their siblings on-line? The > question "Are threads enabled?" doesn't seem to have a simple yes/no > answer. At best you might ask "Does cpu N have any online siblings?" > but the answer to that question could change before you could make > use of the information. > I think you bring up an interesting issue. because of HOTPLUG, I need to register a cpu hotplug notifier to make sure I get called to take the appropriate action. As Christoph is suggesting, it is probably best to hide the variable behind a helper function. Of course, there is still a race between the insertion of the module and a hotplug event. Maybe there is a lock I could grab to serialize this? This reminds me that I have a similar hotplug issue on P4. Thanks -- -Stephane - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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