netdev - Re: [PATCH bpf-next 0/5] introduce bpf

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Message-ID: <CAADnVQ+KVfcU6gvYPmLvPk3-SHwuWEbhttzE24gC0RSCQgxv6g@mail.gmail.com>
Date:   Thu, 2 Dec 2021 18:09:01 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Hou Tao <houtao1@...wei.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>, Yonghong Song <yhs@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next 0/5] introduce bpf_strncmp() helper

On Tue, Nov 30, 2021 at 6:07 AM Hou Tao <houtao1@...wei.com> wrote:
>
> Hi,
>
> The motivation for introducing bpf_strncmp() helper comes from
> two aspects:
>
> (1) clang doesn't always replace strncmp() automatically
> In tracing program, sometimes we need to using a home-made
> strncmp() to check whether or not the file name is expected.
>
> (2) the performance of home-made strncmp is not so good
> As shown in the benchmark in patch #4, the performance of
> bpf_strncmp() helper is 18% or 33% better than home-made strncmp()
> under x86-64 or arm64 when the compared string length is 64. When
> the string length grows to 4095, the performance win will be
> 179% or 600% under x86-64 or arm64.

I think 'home made' strncmp could have been written
differently. I bet in bpf assembly it would be much closer
in performance if not the same,
but the helper is useful.
The patch set doesn't apply cleanly.
Pls respin.