From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from relay.hostedemail.com (smtprelay0010.hostedemail.com [216.40.44.10]) (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 5556328507D; Wed, 18 Jun 2025 15:37:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=216.40.44.10 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750261027; cv=none; b=C1rYg9jpjzZhzHSLXsYuHS5VNBDvMZYF2CcMVRYJ89Xw1p2QCo1Uj5USJBMsnAiTYciL6ozXyisf1pfe6RtBDnTHaXHgl45dMER1C4VCDfKEMTbW6t678akOoDZfK4XM6aJMDN+fAQLvADlNgeJkVeBaxmlBSdxY8iNNLuQJSmM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1750261027; c=relaxed/simple; bh=H4U3Ky+IrsZIJIJLfXMmCz0/Z/sH4WWa+E0A4hZY8gM=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=izXjoiky8caEF4DFKADhuY8M0Hn1B+srfqkl2Q5k9W0V4i9bza9XRyY9SxQpo9FToD98rqjNgnOMw5HpfAIiAt+kWqVn6USoBemcgGrw3kMekLzRnqLQ4JQtuGMJqvK2nr0biTnw7xfedt6tPqcGysklCyfEHXTKyftYNl35JwQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org; spf=pass smtp.mailfrom=goodmis.org; arc=none smtp.client-ip=216.40.44.10 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=goodmis.org Received: from omf13.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id B1C781402DB; Wed, 18 Jun 2025 15:37:02 +0000 (UTC) Received: from [HIDDEN] (Authenticated sender: rostedt@goodmis.org) by omf13.hostedemail.com (Postfix) with ESMTPA id A3AD420010; Wed, 18 Jun 2025 15:36:58 +0000 (UTC) Date: Wed, 18 Jun 2025 11:37:06 -0400 From: Steven Rostedt To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, x86@kernel.org, Masami Hiramatsu , Mathieu Desnoyers , Josh Poimboeuf , Ingo Molnar , Jiri Olsa , Namhyung Kim , Thomas Gleixner , Andrii Nakryiko , Indu Bhagat , "Jose E. Marchesi" , Beau Belgrave , Jens Remus , Linus Torvalds , Andrew Morton Subject: Re: [PATCH v10 06/14] unwind_user/deferred: Add deferred unwinding interface Message-ID: <20250618113706.2eb46544@gandalf.local.home> In-Reply-To: <20250618142000.GS1613376@noisy.programming.kicks-ass.net> References: <20250611005421.144238328@goodmis.org> <20250611010428.770214773@goodmis.org> <20250618142000.GS1613376@noisy.programming.kicks-ass.net> X-Mailer: Claws Mail 3.20.0git84 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: A3AD420010 X-Stat-Signature: je68cw8skeuwinopqsr3tb1eoid8b658 X-Rspamd-Server: rspamout05 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Session-ID: U2FsdGVkX1/YoKH8GuEQ0yQVJuweTy+bFYg7UncVhlQ= X-HE-Tag: 1750261018-678897 X-HE-Meta: U2FsdGVkX19XfgmjSoFRuaBqQl+KSL0/+93MSakFfJdGRZSGhN7pEoSQsJlLVCfByRxxCGivGP4wgp10u5COPglY4NovJUFeQSFbttUk9SrRTfOlMgZ0LrPYVeIkKJcZGS+z8F9mUaP+2c968hzJvVrLWAOC9o9pgNosJa18H/jHmhtMVrBUAwQLM/KT39SHUIjpuUeaQABg0L+kGaMPBk/6Hg9nBoCKlf+4wepjjJNHMqoGzNvxWsPjSuIB5GmhM3dxznDQf+p0gVBueUkYACTOjTWMW1e1WufGgDDccZoeQ4iX7XJ4Qot5Cpykwig4piM0AeJgg5jl4GygO5ZyNFu5wa59XOAZKXFtuVYnif51p3JxgRfHcpCjnpH5unv0 On Wed, 18 Jun 2025 16:20:00 +0200 Peter Zijlstra wrote: > > The timestamp is passed to the caller on request, and when the stacktrace is > > generated upon returning to user space, it call the requester's callback > > with the timestamp as well as the stacktrace. > > This whole story hinges on there being a high resolution time-stamp > available... Good thing we killed x86 !TSC support when we did. You sure > there's no other architectures you're interested in that lack a high res > time source? > > What about two CPUs managing to request an unwind at exactly the same > time? It's mapped to a task. As long as each timestamp is unique for a task it should be fine. As the trace can record the current->pid along with the timestamp to map to the unique user space stack trace. As for resolution, as long as there can't be two system calls back to back within the same time stamp. Otherwise, yeah, we have an issue. -- Steve