Ingo Molnar <mi...@kernel.org> writes: > * Jiri Olsa <jo...@redhat.com> wrote: > >> On Fri, Oct 03, 2014 at 06:34:21AM +0200, Ingo Molnar wrote: >> > >> > * Alexander Yarygin <yary...@linux.vnet.ibm.com> wrote: >> > [..] >> > >> > What's the performance effect of this - i.e. by how much does CPU >> > use increase due to copying the events? >> > >> > Wouldn't it be faster to fix this problem by updating the mmap >> > tail pointer only once the event has truly been consumed? >> >> Alexander mentioned he'd loose data, because of userspace >> processing being to slow: >> >> http://marc.info/?l=linux-kernel&m=141111652424818&w=2 > > So copying helps by allocating an essentially larger buffer, to > hold all unprocessed events that user-space is too slow to > process? > > I guess it's a valid usecase. > > Thanks, > > Ingo
Right. Also, it looks like the overhead here isn't a big deal: time needed for actual processing an event is significantly bigger and the additional memdup() doesn't change that much. -- 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/
