From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qk2-f42.google.com (mail-qk2-f42.google.com [74.125.230.234]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 029DF3B38B9 for ; Thu, 17 Sep 2026 16:35:29 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=74.125.230.234 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789662932; cv=none; b=NB1XsgNbsLgeNyep2Gwr6+Wh2J55TPa7tZhZSvqXOOEQAz6S005dV8xEoFoFK94wmOAYl8OXjcUFbmiVVyBwsuw0SUUXXwuAs9/aTQEEZf1y3RtXlv/6ypq7TxMpC+An+QaEQCzd2wkaOgglOyerXLa7bGXzQ+KtrB5h//K8AsM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789662932; c=relaxed/simple; bh=QgmhQmszRFG/vfc4SQJB1/3XDJxm8LGwggD6bEqDTmg=; h=Date:Message-ID:From:To:Cc:Subject:In-Reply-To:References: MIME-Version:Content-Type; b=g9Dj4/nDhSArVJMaJwDzOJBXtwXDUx0+zTTpdTektl2lU7oujS6PM6Jtx1kcqTH76LKTH7CRgHbOkAdsgMGVHeBqoBMwtO4s7N1Y6TsCidVz0UxXic2qRhHI12C3rfh4vFXJkf2n8g5iZrORcChuuhYDzqTENXZGKiLc7uC4zJI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=toxicpanda.com; spf=pass smtp.mailfrom=toxicpanda.com; dkim=pass (2048-bit key) header.d=toxicpanda.com header.i=@toxicpanda.com header.b=LuM51xkz; arc=none smtp.client-ip=74.125.230.234 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=toxicpanda.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=toxicpanda.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=toxicpanda.com header.i=@toxicpanda.com header.b="LuM51xkz" Received: by mail-qk2-f42.google.com with SMTP id d75a77b69052e-532910016beso8965391cf.2 for ; Thu, 17 Sep 2026 09:35:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=toxicpanda.com; s=google; t=1789662929; x=1790267729; darn=vger.kernel.org; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:subject:cc:to:from:message-id:date:from:to:cc:subject :date:message-id:reply-to:content-type; bh=BF23L7IjgM1pfHyM3ghg4jPhGbV/DtVtyTw2lo+n/XU=; b=LuM51xkzmAaOcyQO6PRPefCD2IUxYQT6stDb8ZVHLROTPhEUuc2vBl4F86rmGvBLPm D9gDj94gfkeOQ8qx3DosrHXRPdS9mtpAzG07684+KfGg4N9ucRAuw0bpthVZkojarv0b sJsMFZXDCEAgJvBZRBiu0kkMv9HtohKo2yc7z5TfhWdj4BStarX6VUMcJpc3ocvi43s4 2a+ot/MLV2YnufdCKmIczlWJ+sAlTm23mkavayZtNtHNuiIkH8Ol/7WNRpf4lLwz3BUo 4LKiQZ4lhAKDfF1efbEIUq1y6ElZII3YzpkzqF2cLv8D926TqKlVlL7qf+ird7QcS6wd eAGw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20260707; t=1789662929; x=1790267729; h=content-transfer-encoding:content-type:mime-version:references :in-reply-to:subject:cc:to:from:message-id:date:x-gm-gg :x-gm-message-state:from:to:cc:subject:date:message-id:reply-to :content-type; bh=BF23L7IjgM1pfHyM3ghg4jPhGbV/DtVtyTw2lo+n/XU=; b=sPFTMc1Fjy6BeSpBvNgILAaLxBJ6Uh9jEfzqLAxD+3xiWMbRiHFhhdWH3Ps+RNu3OO 5UXoXrk3J02QXfeMPTmjJv5h35/6wr+mcRVJLLzpKVhB612EESiUpn7nZKYGQnDmuIym Ut57DvYZgQ6BzY9fcGdAiV7PPH+gABD0+emJtH9dFr+EilReA9n/F8JjuoidLWa53/HA 9kLLUknDEBHAU2yxSmETb/IqETTeCW5B6RmoQecmCgccqnIeOY10f8jsRTT1Wxkj8O/p Q4I9AZPRK7du+WGj0y1rjuP9Aj2sH3yW8NJWHm/goetvSX3uN/Gf+Ybd7p+mr67BmdPq rAQQ== X-Forwarded-Encrypted: i=1; AKwUvBxTCe7/98gIzZpudgIZCtOcGyv/YTuvAa2h0WegdakN2Q7Rn5b45FGO1fH5qNKwtNA/28g=@vger.kernel.org X-Gm-Message-State: AFuF++mI4QUUsmRdoOiB0lYUHzGZPiwv2+bSF5E11+KAoOEXLvOeYBHx 6AaTeOr/UI4NIOQyP9m7j7BaR1yZgwuNpwS/Uca1FtFbrmMm9w69X3Nwuo3tridlMyY= X-Gm-Gg: AYBFou2HmALh3jVFB3CRRHLKAHSrjtv795YYXcttghRSh/wnML8+4QiTkN7Tsyl9+gi MQBcTDv340PatosqzHcNAkgmoWU3PDPMxCBrV88C06H4nqtvNqacQTH+IglKNtaVlM2sMBnnKd2 5DL4cnemn86Usns77AoTZjU0Ox9tbgp9uXyzywUR1kCUjvmUekkZNlpMrwNztt/jb6gCRv8h8EM 5c7w1fusL9w2aYKh2rYSr8ZInzddGTYT6IiKTPBzIoDyyc6BtfNA6z0pOqIK3vHyMHqdhoVbsvE uKRToCHiRmxLrMXAeFwJ0pdd4IWZqjanP6U4JVC0fBGQ/TAl614pLCYWRO05pi7VqPR9uWJARZ6 0tkrqxlxdL4RDvOiJYBtvu9scpc38MBcsfE+Vftm1tcjQh637b5hYXzlsAaVn0f9RSWsCnEb6RW Ml8poD1WFEADxOc3iXVRm8B8IHg4F1eehxHooXQHM/340SbdwocAleDkLRU+fEysKYbA11f9Kn2 X4fnxFzUBRjToFgEXaIgxPsDtlxnKefzrLgcMidKWqByOSSEP6XcNXU X-Received: by 2002:a05:622a:1ba0:b0:530:b2e1:2f3b with SMTP id d75a77b69052e-5329b61d526mr11929121cf.50.1789662928648; Thu, 17 Sep 2026 09:35:28 -0700 (PDT) Received: from toxicpanda.com (ec2-34-228-114-98.compute-1.amazonaws.com. [34.228.114.98]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-5326208ea78sm56756741cf.24.2026.09.17.09.35.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Sep 2026 09:35:27 -0700 (PDT) Date: Thu, 17 Sep 2026 16:35:19 +0000 Message-ID: From: Josef Bacik To: "Paul E. McKenney" , Frederic Weisbecker Cc: Neeraj Upadhyay , Joel Fernandes , Boqun Feng , Thomas Gleixner , Peter Zijlstra , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Jiri Olsa , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , x86@kernel.org, Catalin Marinas , Will Deacon , Puranjay Mohan , Xu Kuohai , Andy Lutomirski , Josh Triplett , Uladzislau Rezki , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Juergen Gross , Luis Chamberlain , Ihor Solodrai , linux-kernel@vger.kernel.org, rcu@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, xen-devel@lists.xenproject.org Subject: Re: [PATCH RFC v3 03/13] rcu-tasks: Add a Tasks RCU implementation for reader-marked trampolines In-Reply-To: <8fea176a-0ca0-4a70-8cf9-8240a22359e4@paulmck-laptop> References: <20260915-b4-rcu-tasks-preempt-qs-v3-0-0ad30c4c5ee7@toxicpanda.com> <20260915-b4-rcu-tasks-preempt-qs-v3-3-0ad30c4c5ee7@toxicpanda.com> <91687748-0781-4133-baed-43cf82f35ff5@paulmck-laptop> <6afb0afe-e7b8-46b4-9fea-2c7cf4791044@paulmck-laptop> <8b73e1b3-0580-4ba9-b2e0-6363e429808d@paulmck-laptop> <8fea176a-0ca0-4a70-8cf9-8240a22359e4@paulmck-laptop> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On Thu, 17 Sep 2026 08:40:10 -0700, Paul E. McKenney wrote: > On Thu, Sep 17, 2026 at 02:14:57PM +0200, Frederic Weisbecker wrote: > > You're right. So we'll indeed need to reuse the deferred qs points here. > > Except this is getting a bit involved. > > Don't get me wrong, if Josef is happy to take this on, far be it from me > to stand in his way. But if not, we should be willing to treat this > optimization as a follow-on effort, whether by Josef or someone else. Follow-on works for me. For what it's worth 03/13 is already fairly close to what Frederic describes, just outside the core flavor: no task-list scan (the GP waits per CPU for a pass through __schedule() or an EQS), the irq-exit preemption path checks the interrupted IP and queues the task as a holdout before the switch, and the holdout is keyed on where the task was interrupted so nothing is needed from the trampoline tail. Moving that IP check into the tick / rcu_exp_handler() / deferred-QS paths and reusing the blocked-tasks list is something I'm happy to look at once this has settled. v4 will pick up Alexei's ask (reader emitted by the BPF JIT around the fentry and fexit regions rather than in the glue) and the idle-CPU hole Sashiko found. Thanks, Josef