linux-kernel - Re: [PATCH net-next v3 6/8] bpf: cpumap: switch to napi_skb_cache_get

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Message-ID: <874j1xoave.fsf@toke.dk>
Date: Fri, 17 Jan 2025 13:58:29 +0100
From: Toke Høiland-Jørgensen <toke@...hat.com>
To: Alexander Lobakin <aleksander.lobakin@...el.com>, Andrew Lunn
 <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo
 Abeni <pabeni@...hat.com>
Cc: Alexander Lobakin <aleksander.lobakin@...el.com>, Lorenzo Bianconi
 <lorenzo@...nel.org>, Daniel Xu <dxu@...uu.xyz>, Alexei Starovoitov
 <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko
 <andrii@...nel.org>, John Fastabend <john.fastabend@...il.com>, Jesper
 Dangaard Brouer <hawk@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, netdev@...r.kernel.org, bpf@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next v3 6/8] bpf: cpumap: switch to
 napi_skb_cache_get_bulk()

Alexander Lobakin <aleksander.lobakin@...el.com> writes:

> Now that cpumap uses GRO, which drops unused skb heads to the NAPI
> cache, use napi_skb_cache_get_bulk() to try to reuse cached entries
> and lower MM layer pressure. Always disable the BH before checking and
> running the cpumap-pinned XDP prog and don't re-enable it in between
> that and allocating an skb bulk, as we can access the NAPI caches only
> from the BH context.
> The better GRO aggregates packets, the less new skbs will be allocated.
> If an aggregated skb contains 16 frags, this means 15 skbs were returned
> to the cache, so next 15 skbs will be built without allocating anything.
>
> The same trafficgen UDP GRO test now shows:
>
>                 GRO off   GRO on
> threaded GRO    2.3       4         Mpps
> thr bulk GRO    2.4       4.7       Mpps
> diff            +4        +17       %
>
> Comparing to the baseline cpumap:
>
> baseline        2.7       N/A       Mpps
> thr bulk GRO    2.4       4.7       Mpps
> diff            -11       +74       %
>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> Tested-by: Daniel Xu <dxu@...uu.xyz>

Reviewed-by: Toke Høiland-Jørgensen <toke@...hat.com>