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Message-ID: <b18fdfc3-987d-9351-ca6c-5d4cb2d71af1@linux.dev> Date: Thu, 18 May 2023 09:51:39 -0700 From: Martin KaFai Lau <martin.lau@...ux.dev> To: paulmck@...nel.org 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 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.
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