Messages in this thread | | | From | Alexander Yarygin <> | Subject | Re: [PATCH 1/2] perf tools: Add option to copy events when queueing | Date | Fri, 03 Oct 2014 18:25:15 +0400 |
| |
Ingo Molnar <mingo@kernel.org> writes:
> * Jiri Olsa <jolsa@redhat.com> wrote: > >> On Fri, Oct 03, 2014 at 06:34:21AM +0200, Ingo Molnar wrote: >> > >> > * Alexander Yarygin <yarygin@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.
| |