From: "Toke Høiland-Jørgensen" <toke@redhat.com>
To: Jesper Dangaard Brouer <brouer@redhat.com>,
Tariq Toukan <ttoukan.linux@gmail.com>,
Daniel Borkmann <borkmann@iogearbox.net>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii.nakryiko@gmail.com>,
bpf@vger.kernel.org
Cc: Jesper Dangaard Brouer <brouer@redhat.com>,
Tariq Toukan <tariqt@nvidia.com>,
gal@nvidia.com, lorenzo@kernel.org, netdev@vger.kernel.org,
echaudro@redhat.com, andrew.gospodarek@broadcom.com
Subject: Re: [PATCH bpf-next V2] bpf/xdp: optimize bpf_xdp_pointer to avoid reading sinfo
Date: Thu, 01 Jun 2023 22:37:31 +0200 [thread overview]
Message-ID: <87bkhydilw.fsf@toke.dk> (raw)
In-Reply-To: <168563651438.3436004.17735707525651776648.stgit@firesoul>
Jesper Dangaard Brouer <brouer@redhat.com> writes:
> Currently we observed a significant performance degradation in
> samples/bpf xdp1 and xdp2, due XDP multibuffer "xdp.frags" handling,
> added in commit 772251742262 ("samples/bpf: fixup some tools to be able
> to support xdp multibuffer").
>
> This patch reduce the overhead by avoiding to read/load shared_info
> (sinfo) memory area, when XDP packet don't have any frags. This improves
> performance because sinfo is located in another cacheline.
>
> Function bpf_xdp_pointer() is used by BPF helpers bpf_xdp_load_bytes()
> and bpf_xdp_store_bytes(). As a help to reviewers, xdp_get_buff_len() can
> potentially access sinfo, but it uses xdp_buff_has_frags() flags bit check
> to avoid accessing sinfo in no-frags case.
>
> The likely/unlikely instrumentation lays out asm code such that sinfo
> access isn't interleaved with no-frags case (checked on GCC 12.2.1-4).
> The generated asm code is more compact towards the no-frags case.
>
> The BPF kfunc bpf_dynptr_slice() also use bpf_xdp_pointer(). Thus, it
> should also take effect for that.
>
> Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Thanks for fixing this!
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
next prev parent reply other threads:[~2023-06-01 20:37 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-06-01 16:21 [PATCH bpf-next V2] bpf/xdp: optimize bpf_xdp_pointer to avoid reading sinfo Jesper Dangaard Brouer
2023-06-01 20:34 ` Lorenzo Bianconi
2023-06-05 20:41 ` Alexei Starovoitov
2023-06-01 20:37 ` Toke Høiland-Jørgensen [this message]
2023-06-05 20:50 ` patchwork-bot+netdevbpf
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