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Message-ID: <2cc44c11-bcdc-4ae4-a42d-d6d46cf1da6e@paulmck-laptop> Date: Thu, 18 May 2023 10:25:05 -0700 From: "Paul E. McKenney" <paulmck@...nel.org> To: Martin KaFai Lau <martin.lau@...ux.dev> Cc: Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, bpf@...r.kernel.org, netdev@...r.kernel.org Subject: Re: [PATCH bpf] Use call_rcu_hurry() with synchronize_rcu_mult() 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
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