On Monday 30 March 2015 03:06 PM, Michael Ellerman wrote: > On Sun, 2015-22-03 at 04:42:57 UTC, "Shreyas B. Prabhu" wrote: >> Currently, cpu_online_cores_map returns a mask, which for every core >> that has atleast one online thread, has the first-cpu-of-that-core's bit >> set. > > ... which for every core with at least one online thread, has the bit for > thread 0 of the core set to 1, and the bits for all other threads of the > core > set to 0. > > Maybe that's clearer? > >> But the first cpu itself may not be online always. In such cases, if > ^ > of the core > >> the returned mask is used for IPI, then it'll cause IPIs to be skipped >> on cores where the first thread is offline. > > .. because the IPI code refuses to send IPIs to offline threads, right?
Yes. > >> Fix this by setting first-online-cpu-of-the-core's bit in the mask. > > .. by setting the bit of the first online thread in the core. > >> This is done by fixing this in the underlying function >> cpu_thread_mask_to_cores. > > > The result has the property that for all cores with online threads, there is > one bit set in the returned map. And further, all bits that are set in the > returned map correspond to online threads. > > >> Signed-off-by: Shreyas B. Prabhu <shre...@linux.vnet.ibm.com> >> --- >> This patch is new in v3 >> >> In an example scenario where all the threads of 1st core are offline >> and argument to cpu_thread_mask_to_cores is cpu_possible_mask, >> with this implementation, return value will not have any bit >> corresponding to 1st core set. I think that should be okay. Any thoughts? > > Looking at linux-next: > > $ git grep cpu_thread_mask_to_cores > arch/powerpc/include/asm/cputhreads.h:/* cpu_thread_mask_to_cores - Return > a cpumask of one per cores > arch/powerpc/include/asm/cputhreads.h:static inline cpumask_t > cpu_thread_mask_to_cores(const struct cpumask *threads) > arch/powerpc/include/asm/cputhreads.h: return > cpu_thread_mask_to_cores(cpu_online_mask); > $ git grep cpu_online_cores_map > arch/powerpc/include/asm/cputhreads.h:static inline cpumask_t > cpu_online_cores_map(void) > > ie. There are no users. > > So yeah I think we can change the semantics of this, and the semantics you > describe make sense. > > If you agree with my changelog comments I'm happy to fix that up and merge > this, or you can send a v4 if you like. > I'll fix the changelog in v4. > cheers > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
