netdev - Re: [PATCH v3 net-next 14/15] net: Reference bpf_redirect_info via task_struct on PREEMPT

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Date: Wed, 05 Jun 2024 12:37:36 +0200
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Jesper Dangaard Brouer <hawk@...nel.org>, Sebastian Andrzej Siewior
 <bigeasy@...utronix.de>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, "David S. Miller"
 <davem@...emloft.net>, Boqun Feng <boqun.feng@...il.com>, Daniel Borkmann
 <daniel@...earbox.net>, Eric Dumazet <edumazet@...gle.com>, Frederic
 Weisbecker <frederic@...nel.org>, Ingo Molnar <mingo@...hat.com>, Jakub
 Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Peter
 Zijlstra <peterz@...radead.org>, Thomas Gleixner <tglx@...utronix.de>,
 Waiman Long <longman@...hat.com>, Will Deacon <will@...nel.org>, Alexei
 Starovoitov <ast@...nel.org>, Andrii Nakryiko <andrii@...nel.org>, Eduard
 Zingerman <eddyz87@...il.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa
 <jolsa@...nel.org>, John Fastabend <john.fastabend@...il.com>, KP Singh
 <kpsingh@...nel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, Song Liu
 <song@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Yonghong Song
 <yonghong.song@...ux.dev>, bpf@...r.kernel.org
Subject: Re: [PATCH v3 net-next 14/15] net: Reference bpf_redirect_info via
 task_struct on PREEMPT_RT.

Jesper Dangaard Brouer <hawk@...nel.org> writes:

> On 31/05/2024 12.38, Sebastian Andrzej Siewior wrote:
>> On 2024-05-30 00:09:21 [+0200], Toke Høiland-Jørgensen wrote:
>>> [...]
>>>> @@ -240,12 +240,14 @@ static int cpu_map_bpf_prog_run(struct bpf_cpu_map_entry *rcpu, void **frames,
>>>>   				int xdp_n, struct xdp_cpumap_stats *stats,
>>>>   				struct list_head *list)
>>>>   {
>>>> +	struct bpf_net_context __bpf_net_ctx, *bpf_net_ctx;
>>>>   	int nframes;
>  >>
>>> I think we need to zero-initialise all the context objects we allocate
>>> on the stack.
>>>
>> Okay, I can do that.
>
> Hmm, but how will this affect performance?

My hunch would be that this would be in a cache line we're touching
anyway, so it won't make much difference? But better measure, I suppose :)

-Toke