From: Yonghong Song <yhs@fb.com>
To: Song Liu <song@kernel.org>
Cc: bpf <bpf@vger.kernel.org>, Networking <netdev@vger.kernel.org>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Kernel Team <kernel-team@fb.com>, Martin KaFai Lau <kafai@fb.com>
Subject: Re: [PATCH bpf-next] bpf: using rcu_read_lock for bpf_sk_storage_map iterator
Date: Mon, 14 Sep 2020 22:25:23 -0700 [thread overview]
Message-ID: <86ee274b-a23c-25aa-6ec3-e1448667b6b4@fb.com> (raw)
In-Reply-To: <CAPhsuW6+kqJ+=+ssxdZ7+ZsCgiUC2rrLPZsWb6YdXEiN7ZhW9Q@mail.gmail.com>
On 9/14/20 2:28 PM, Song Liu wrote:
> On Mon, Sep 14, 2020 at 11:47 AM Yonghong Song <yhs@fb.com> wrote:
>>
>> Currently, we use bucket_lock when traversing bpf_sk_storage_map
>> elements. Since bpf_iter programs cannot use bpf_sk_storage_get()
>> and bpf_sk_storage_delete() helpers which may also grab bucket lock,
>> we do not have a deadlock issue which exists for hashmap when
>> using bucket_lock ([1]).
>
> The paragraph above describes why we can use bucket_lock, which is more
> or less irrelevant to this change. Also, I am not sure why we refer to [1] here.
What I try to clarify here is unlike [1], we do not have bugs
with the current code.
But I guess no bugs is implicit so I probably do not need to say
anything. Will skip the above paragraph in the next revision.
>
>>
>> If a bucket contains a lot of sockets, during bpf_iter traversing
>> a bucket, concurrent bpf_sk_storage_{get,delete}() may experience
>> some undesirable delays. Using rcu_read_lock() is a reasonable
>
> It will be great to include some performance comparison.
Sure. Let me give some try to collect some statistics.
>
>> compromise here. Although it may lose some precision, e.g.,
>> access stale sockets, but it will not hurt performance of other
>> bpf programs.
>>
>> [1] https://lore.kernel.org/bpf/20200902235341.2001534-1-yhs@fb.com
>>
>> Cc: Martin KaFai Lau <kafai@fb.com>
>> Signed-off-by: Yonghong Song <yhs@fb.com>
>
> Other than these,
>
> Acked-by: Song Liu <songliubraving@fb.com>
>
> [...]
>
next prev parent reply other threads:[~2020-09-15 5:26 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-14 18:46 [PATCH bpf-next] bpf: using rcu_read_lock for bpf_sk_storage_map iterator Yonghong Song
2020-09-14 21:28 ` Song Liu
2020-09-15 5:25 ` Yonghong Song [this message]
2020-09-15 15:33 ` Jakub Kicinski
2020-09-15 17:35 ` Yonghong Song
2020-09-15 17:40 ` Jakub Kicinski
2020-09-15 18:56 ` Yonghong Song
2020-09-15 19:03 ` Alexei Starovoitov
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