From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id CF0CD1C1F18; Fri, 8 Nov 2024 22:26:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731104799; cv=none; b=C1T/T0J9rrNuxh/7OmuQGEV0mTmq6SEmQ0rVrnCtq0PV4/LVug1qzERGHVemREOj8kROeoFMFvPX6+UP8gSniQeO7ivHqBjs+BZE1bwjFYvf6Xg/bXWfHE/MmRO1bwECL3VPRqEYLTcgSuPL/3sbQYBxqf8aHRitwwj7wapAmRg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1731104799; c=relaxed/simple; bh=VyvMOyH0+82bfFFSDpJF4HQhtVh841gbibWXKNpthTQ=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=KDwADDGxlsXDsrqAwXHt8U/XnqtDtXMdMKb33j9nD5yo4w/iddO8Bia1pWtAdUeYg2YjsmcQbN/mLPZWzzdGcB4qCS7HTCYI20IZpKb1/iDxO8dA4V9PeLD6vtMUPfRJ9Ow4TlwGqm2WDidJSmTrire949x0nagDmbnw/X4uESc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mzUx1o8+; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mzUx1o8+" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CE86BC4CECD; Fri, 8 Nov 2024 22:26:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1731104799; bh=VyvMOyH0+82bfFFSDpJF4HQhtVh841gbibWXKNpthTQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=mzUx1o8+vz9jW9xR/5GwKQShCqqK+tBfE6NaeFxSENGxLtY9tMqVAszbC/dDBebX6 cK7iNO32eMnCkxFccZhMYO9CTm6cEhGVYeElzHZF8rza039d0Xxd61ydvGnvmfCJ4Z pQqXL5SGIO89nztTS0lUv8ZzvBJhCDkLjfV+BDEjgMoH0MVMlIhExl/eD5as5kj09A qo0OLnvpWdhNpxPOMONM/ttPA57IQNfzV8SvgkXoB+jpEYyhLxs7p/z/xQB2FrK67L 8fChkSxIi+Xgws4KAC9eO8EmlJlDyW7OiDObAFdyeocDIWDaOCL+M7wvYXzaJdWho2 mXkQ6/9sDEIDw== Date: Fri, 8 Nov 2024 23:26:36 +0100 From: Frederic Weisbecker To: Oleg Nesterov Cc: Sebastian Andrzej Siewior , "Lai, Yi" , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org, Adrian Hunter , Alexander Shishkin , Arnaldo Carvalho de Melo , Daniel Bristot de Oliveira , Ian Rogers , Ingo Molnar , Jiri Olsa , Kan Liang , Marco Elver , Mark Rutland , Namhyung Kim , Peter Zijlstra , Thomas Gleixner , Arnaldo Carvalho de Melo , yi1.lai@intel.com, syzkaller-bugs@googlegroups.com Subject: Re: [PATCH v4 2/6] perf: Enqueue SIGTRAP always via task_work. Message-ID: References: <20240624152732.1231678-1-bigeasy@linutronix.de> <20240624152732.1231678-3-bigeasy@linutronix.de> <20241029172126.5XY8vLBH@linutronix.de> <20241030140721.pZzb9D-u@linutronix.de> <20241107144617.MjCWysud@linutronix.de> <20241108190835.GA11231@redhat.com> Precedence: bulk X-Mailing-List: linux-perf-users@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20241108190835.GA11231@redhat.com> Le Fri, Nov 08, 2024 at 08:08:36PM +0100, Oleg Nesterov a écrit : > Sorry, currently I don't have time to even read the emails from lkml. > > Plus I wasn't cc'ed so I don't understand the intent at all, but ... > > On 11/08, Frederic Weisbecker wrote: > > > > > @@ -232,13 +222,24 @@ void task_work_run(void) > > > * But it can remove another entry from the ->next list. > > > */ > > > raw_spin_lock_irq(&task->pi_lock); > > > + do { > > > + head = NULL; > > > + if (work) { > > > + head = READ_ONCE(work->next); > > > + } else { > > > + if (task->flags & PF_EXITING) > > > + head = &work_exited; > > > + else > > > + break; > > > + } > > > + } while (!try_cmpxchg(&task->task_works, &work, head)); > > > raw_spin_unlock_irq(&task->pi_lock); > > > > And having more than one task work should be sufficiently rare > > that we don't care about doing the locking + cmpxchg() for each > > of them pending. > > Please see > https://lore.kernel.org/all/1440816150.8932.123.camel@edumazet-glaptop2.roam.corp.google.com/ > and the whole thread. > > I don't think raw_spin_lock_irq + cmpxchg for each work is a good > idea, but quite possibly I misunderstood this change. I did not realize there could be gazillion files released in a row. So there could be noticeable performance issues I guess... Thanks. > > Oleg. >