From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kylehuey.com header.i=@kylehuey.com header.b="OwGcd7y/" Received: from mail-ej1-x62c.google.com (mail-ej1-x62c.google.com [IPv6:2a00:1450:4864:20::62c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D42FA1BD for ; Tue, 5 Dec 2023 10:23:43 -0800 (PST) Received: by mail-ej1-x62c.google.com with SMTP id a640c23a62f3a-a1a0bc1e415so563028566b.0 for ; Tue, 05 Dec 2023 10:23:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kylehuey.com; s=google; t=1701800622; x=1702405422; darn=vger.kernel.org; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:from:to:cc:subject:date :message-id:reply-to; bh=v+0YlV3bBjMI57c/U4EB7oIqdJ8ldlbudM2aWbhqhfU=; b=OwGcd7y/rv/7lEe1ubMO6IEKyPg7ia2YgVEA50a9URa6nktRIzuMWBTslrYMTj0IPS 1Ur1dbbODFAhoyF9OYZKYFP9707UxeEnxuE/ciLDebn31FlkscteI2flGj/QTYH/fDya cglI6gszPsw2Cv88t6yTcI+vr8bwBKrAI2x76562sGnte1+jxeBx4+0RwyneXrDY3s0d 1bM9bGNVKz8q2MVjuoaLbGi9cUsxxb6Crs8iwz/XEJOvaniMAEAJK+nWqTLgVwjFh1ea lr6KVtHNflooM0mdmqkIveAXTdotK/74xkjIGpwHwm6A8mnsW9d32pg8Y437ATeraKgr dlEA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701800622; x=1702405422; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=v+0YlV3bBjMI57c/U4EB7oIqdJ8ldlbudM2aWbhqhfU=; b=sc1dCpQwzsOw5Tf6Cjvp33zlH3XPPPciMEc5JOSD9Cy3ZO51HdF9ZP+oxnGTuSAZAL T8C1zR/StSlXRy+L6oGqT4nJ/ZGCHFettoYgucNremQc4RAhYjZLwLstqG8B2w6Jp+8z 6aSG4TZ1SPRX7wdWuXLR2vdDSL+nQ3D6/T/XIImyORrBYm2uiAt28EPxsoea6HZXbiVU VZbtS+LZlu+W4YJUZ0gP+ft2I84ksr55u4gaIrccHzikgwYyyvN1FQvLlC8piYWBME7w CYcGVTNJecY2VVK6yNQZh9VtTXeXlA5g4+56IEFagE76Cx9gAlvIGyVEvrhotl8uvImP XImw== X-Gm-Message-State: AOJu0Yy3K/TxE6b4JQF1WE9rF2CImghF/vXw6xW2vASCtE5I5xp1cvIA kqy6m12tvecl44jPxhNVRFsuhqsKP+behR/ygsZqbQ== X-Google-Smtp-Source: AGHT+IGRGeCn9pEqVAY8iz3lyzXrueW4v8n436DdU9IWtnh+NqFaWgvKvAL5wFhMr6ZBk6uovrD180nlBRzfvUfE5rQ= X-Received: by 2002:a17:906:1003:b0:a1b:81c6:3900 with SMTP id 3-20020a170906100300b00a1b81c63900mr1503399ejm.80.1701800621992; Tue, 05 Dec 2023 10:23:41 -0800 (PST) Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 References: <20231204201406.341074-1-khuey@kylehuey.com> <20231204201406.341074-2-khuey@kylehuey.com> In-Reply-To: From: Kyle Huey Date: Tue, 5 Dec 2023 10:23:30 -0800 Message-ID: Subject: Re: [PATCH 1/2] perf/bpf: Allow a bpf program to suppress I/O signals. To: Marco Elver Cc: Namhyung Kim , Jiri Olsa , Andrii Nakryiko , Kyle Huey , linux-kernel@vger.kernel.org, "Robert O'Callahan" , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Ian Rogers , Adrian Hunter , linux-perf-users@vger.kernel.org, bpf@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Tue, Dec 5, 2023 at 10:17=E2=80=AFAM Marco Elver wrot= e: > > On Tue, 5 Dec 2023 at 19:07, Namhyung Kim wrote: > > > > Hello, > > > > Add Marco Elver to CC. > > > > On Tue, Dec 5, 2023 at 3:16=E2=80=AFAM Jiri Olsa w= rote: > > > > > > On Mon, Dec 04, 2023 at 02:18:49PM -0800, Andrii Nakryiko wrote: > > > > On Mon, Dec 4, 2023 at 12:14=E2=80=AFPM Kyle Huey = wrote: > > > > > > > > > > Returning zero from a bpf program attached to a perf event alread= y > > > > > suppresses any data output. This allows it to suppress I/O availa= bility > > > > > signals too. > > > > > > > > make sense, just one question below > > > > > > > > > > > > > > Signed-off-by: Kyle Huey > > > > > > Acked-by: Jiri Olsa > > > > > > > > --- > > > > > kernel/events/core.c | 4 +++- > > > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > > > > index b704d83a28b2..34d7b19d45eb 100644 > > > > > --- a/kernel/events/core.c > > > > > +++ b/kernel/events/core.c > > > > > @@ -10417,8 +10417,10 @@ static void bpf_overflow_handler(struct = perf_event *event, > > > > > rcu_read_unlock(); > > > > > out: > > > > > __this_cpu_dec(bpf_prog_active); > > > > > - if (!ret) > > > > > + if (!ret) { > > > > > + event->pending_kill =3D 0; > > > > > return; > > > > > + } > > > > > > > > What's the distinction between event->pending_kill and > > > > event->pending_wakeup? Should we do something about pending_wakeup? > > > > Asking out of complete ignorance of all these perf specifics. > > > > > > > > > > I think zeroing pending_kill is enough.. when it's set the perf code > > > sets pending_wakeup to call perf_event_wakeup in irq code that wakes > > > up event's ring buffer readers and sends sigio if pending_kill is set > > > > Right, IIUC pending_wakeup is set by the ring buffer code when > > a task is waiting for events and it gets enough events (watermark). > > So I think it's good for ring buffer to manage the pending_wakeup. > > > > And pending_kill is set when a task wants a signal delivery even > > without getting enough events. Clearing pending_kill looks ok > > to suppress normal signals but I'm not sure if it's ok for SIGTRAP. > > > > If we want to handle returning 0 from bpf as if the event didn't > > happen, I think SIGTRAP and event_limit logic should be done > > after the overflow handler depending on pending_kill or something. > > I'm not sure which kernel version this is for, but in recent kernels, > the SIGTRAP logic was changed to no longer "abuse" event_limit, and > uses its own "pending_sigtrap" + "pending_work" (on reschedule > transitions). > > Thanks, > -- Marco The patch was prepared against a 6.7 release candidate. - Kyle