On Fri, 2009-10-23 at 14:56 +0200, Stephane Eranian wrote: > This patch fixes the default watermark value for > the sampling buffer. With the existing calculation > (watermark = max(PAGE_SIZE, max_size / 2)), no > notification was ever received when the buffer was > exactly 1 page. This was because you would never > cross the threshold (there is no partial samples).
Right, silly thinko, thanks for catching this. > In certain configuration, there was no possibilty > detecting the problem because there was not enough > space left to store the LOST record.In fact, there > may be a more generic problem here. The kernel should > ensure that there is alaways enough space to store > one LOST record. It tries to prepend LOST records for each new event (when there is data lost), so as soon as it manages to write a new event, it will include a LOST record when appropriate. > This patch sets the default watermark to half the > buffer size. With such limit, we are guaranteed to > get a notification even with a single page buffer > assuming no sample is bigger than a page. > > Signed-off-by: Stephane Eranian <eran...@gmail.com> Acked-by: Peter Zijlstra <a.p.zijls...@chello.nl> > --- > kernel/perf_event.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/perf_event.c b/kernel/perf_event.c > index a69d4ed..e8ec4b7 100644 > --- a/kernel/perf_event.c > +++ b/kernel/perf_event.c > @@ -2315,7 +2315,7 @@ perf_mmap_data_init(struct perf_event *event, struct > perf_mmap_data *data) > } > > if (!data->watermark) > - data->watermark = max_t(long, PAGE_SIZE, max_size / 2); > + data->watermark = max_size / 2; > > > rcu_assign_pointer(event->data, data); ------------------------------------------------------------------------------ Let Crystal Reports handle the reporting - Free Crystal Reports 2008 30-Day trial. Simplify your report design, integration and deployment - and focus on what you do best, core application coding. Discover what's new with Crystal Reports now. http://p.sf.net/sfu/bobj-july _______________________________________________ perfmon2-devel mailing list perfmon2-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/perfmon2-devel
