netdev - Re: [PATCH bpf] bpf, test_run: fix &xdp_frame misplacement for LIVE

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Date:   Fri, 10 Feb 2023 14:19:19 +0100
From:   Alexander Lobakin <alexandr.lobakin@...el.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Jakub Kicinski <kuba@...nel.org>, <bpf@...r.kernel.org>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf] bpf, test_run: fix &xdp_frame misplacement for
 LIVE_FRAMES

From: Alexander Lobakin <alexandr.lobakin@...el.com>
Date: Fri, 10 Feb 2023 13:31:28 +0100

> From: Toke Høiland-Jørgensen <toke@...hat.com>
> Date: Thu, 09 Feb 2023 21:58:07 +0100
> 
>> Alexander Lobakin <alexandr.lobakin@...el.com> writes:

[...]

>> Hmm, IIRC my reasoning was that both those cache lines will be touched
>> by the code in xdp_test_run_batch(), so it wouldn't matter? But if
>> there's a performance benefit I don't mind adding an explicit alignment
>> annotation, certainly!
> 
> Let me retest both ways and will see. I saw some huge CPU loads on
> reading xdpf in ice_xdp_xmit(), so that was my first thought.

No visible difference in perf and CPU load... Ok, aligning isn't worth it.

> 
>>
>>> (but in bpf-next probably)
>>
>> Yeah...
>>
>> -Toke
>>
Olek