From: "Paul E. McKenney" <paulmck@kernel.org>
To: Martin KaFai Lau <martin.lau@linux.dev>
Cc: Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Andrii Nakryiko <andrii@kernel.org>, Song Liu <song@kernel.org>,
Yonghong Song <yhs@fb.com>,
John Fastabend <john.fastabend@gmail.com>,
KP Singh <kpsingh@kernel.org>,
Stanislav Fomichev <sdf@google.com>, Hao Luo <haoluo@google.com>,
Jiri Olsa <jolsa@kernel.org>,
bpf@vger.kernel.org, netdev@vger.kernel.org
Subject: Re: [PATCH bpf] Use call_rcu_hurry() with synchronize_rcu_mult()
Date: Thu, 18 May 2023 10:25:05 -0700 [thread overview]
Message-ID: <2cc44c11-bcdc-4ae4-a42d-d6d46cf1da6e@paulmck-laptop> (raw)
In-Reply-To: <b18fdfc3-987d-9351-ca6c-5d4cb2d71af1@linux.dev>
On Thu, May 18, 2023 at 09:51:39AM -0700, Martin KaFai Lau wrote:
> On 5/18/23 7:47 AM, Paul E. McKenney wrote:
> > The bpf_struct_ops_map_free() function must wait for both an RCU grace
> > period and an RCU Tasks grace period, and so it passes call_rcu() and
> > call_rcu_tasks() to synchronize_rcu_mult(). This works, but on ChromeOS
> > and Android platforms call_rcu() can have lazy semantics, resulting in
> > multi-second delays between call_rcu() invocation and invocation of the
> > corresponding callback.
> >
> > Therefore, substitute call_rcu_hurry() for call_rcu().
>
> My understanding on the net-effect is to free up the struct_ops resources faster.
>
> I believe call_rcu() should be fine. struct_ops freeing should not happen
> very often. For example, when a bpf written tcp congestion control
> (struct_ops) is registered, it will stay in the kernel for a long time. A
> couple seconds delay in releasing the struct_ops should be acceptable.
Very good, and sorry for the noise!
Thanx, Paul
prev parent reply other threads:[~2023-05-18 17:25 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-18 14:47 [PATCH bpf] Use call_rcu_hurry() with synchronize_rcu_mult() Paul E. McKenney
2023-05-18 16:51 ` Martin KaFai Lau
2023-05-18 17:25 ` Paul E. McKenney [this message]
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