linux-kernel - Re: [PATCH v2] bpf: Allocate bpf_event

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Message-ID: <CAM9d7cgDcczbo9s+J9TpoQhfHCTeJws=L5bpV458rbo4WTi-aQ@mail.gmail.com>
Date: Wed, 29 May 2024 11:27:17 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Jiri Olsa <olsajiri@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, 
	LKML <linux-kernel@...r.kernel.org>, bpf <bpf@...r.kernel.org>, 
	Aleksei Shchekotikhin <alekseis@...gle.com>, Nilay Vaish <nilayvaish@...gle.com>
Subject: Re: [PATCH v2] bpf: Allocate bpf_event_entry with node info

Hi Alexei,

On Wed, May 29, 2024 at 10:23 AM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Wed, May 29, 2024 at 9:54 AM Namhyung Kim <namhyung@...nel.org> wrote:
> >
> > Hi Jiri,
> >
> > On Wed, May 29, 2024 at 1:31 AM Jiri Olsa <olsajiri@...il.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.
>
> I have the same concern as Jiri.
> Without numbers this is just a code churn.
> Does this patch really make a difference?
> Without numbers maintainers would have to believe the "just trust me" part.
> So..
> pw-bot: cr

Ok, then I'll come back with numbers later.

Thanks,
Namhyung