Re: [PATCH v2] bpf: Allocate bpf_event_entry with node info

Namhyung Kim
2024-05-29T16:54:24Z

Hi Jiri,

On Wed, May 29, 2024 at 1:31 AM Jiri Olsa <olsajiri@gmail.com> wrote:
>
> On Tue, May 28, 2024 at 11:53:11PM -0700, Namhyung Kim wrote:
> > It was reported that accessing perf_event map entry caused pretty high
> > LLC misses in get_map_perf_counter(). As reading perf_event is allowed
> > for the local CPU only, I think we can use the target CPU of the event
> > as hint for the allocation like in perf_event_alloc() so that the event
> > and the entry can be in the same node at least.
>
> looks good, is there any profile to prove the gain?

No, at this point. I'm not sure if it'd help LLC hit ratio but
I think it should improve the memory latency.

Thanks,
Namhyung

>
> >
> > Reported-by: Aleksei Shchekotikhin <alekseis@google.com>
> > Reported-by: Nilay Vaish <nilayvaish@google.com>
> > Signed-off-by: Namhyung Kim <namhyung@kernel.org>
>
> > ---
> > v2) fix build errors
> >
> > kernel/bpf/arraymap.c | 11 +++++++++--
> > 1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
> > index feabc0193852..067f7cf27042 100644
> > --- a/kernel/bpf/arraymap.c
> > +++ b/kernel/bpf/arraymap.c
> > @@ -1194,10 +1194,17 @@ static struct bpf_event_entry *bpf_event_entry_gen(struct file *perf_file,
> > struct file *map_file)
> > {
> > struct bpf_event_entry *ee;
> > + struct perf_event *event = perf_file->private_data;
> > + int node = -1;
> >
> > - ee = kzalloc(sizeof(*ee), GFP_KERNEL);
> > +#ifdef CONFIG_PERF_EVENTS
> > + if (event->cpu >= 0)
> > + node = cpu_to_node(event->cpu);
> > +#endif
> > +
> > + ee = kzalloc_node(sizeof(*ee), GFP_KERNEL, node);
> > if (ee) {
> > - ee->event = perf_file->private_data;
> > + ee->event = event;
> > ee->perf_file = perf_file;
> > ee->map_file = map_file;
> > }
> > --
> > 2.45.1.288.g0e0cd299f1-goog
> >