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 18D9D25CC73; Tue, 20 May 2025 23:26:09 +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=1747783570; cv=none; b=f/UXKYUJ5+2S1Es7+VeshTQj5Ivxm6gNirms1pGimo1i5IZuBVX5GDo9n1ZRtIKsPbFSbA9qg28T4laRL/fue3V4ZL/oDR9Qhl9EJf0Yv8gcF1NTmalRmw40F4+GdN+0xjB/GGaTjO5aVpEpxb1FKNrbyI2XCxO84qeuAoYB8lk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1747783570; c=relaxed/simple; bh=E1ZGX7mjtvtFpechp+ozrWQKmmJfrP8auppqbj8TNPk=; h=Date:From:To:Cc:Subject:Message-Id:In-Reply-To:References: Mime-Version:Content-Type; b=SCbJObsJe1pTIkg8O1TanLXfI9pFBKUJBs8Q1Z/DrAsmnv72r8D493En17OdPFqDbHoZ+B2okgXH8d4nHcwK5iXgYkCKc32hyggyWF4zP2Lbm3ZMO1HBBSwvK4VfZ8VYigpchX67BfkeZHR9k3iszuAjyviv+7qeeMTiHV++apc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RpceNWV/; 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="RpceNWV/" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 345C0C4CEE9; Tue, 20 May 2025 23:26:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1747783569; bh=E1ZGX7mjtvtFpechp+ozrWQKmmJfrP8auppqbj8TNPk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=RpceNWV/vzujP6ckRNkuYvJlrjIqYVzZxmLVsbhekdpSUnuZ0kUTlWW3nnCMcfUfs JqZXpS1NytxfFT3oSFjWHiIuAQ0j/On7uB3f8y+MJCAO85FwR8ChlCDpF9QMylCuVR Om+IeDiQnpW/MEBYklLS6S3qVgTVAIApmpLROdC4QidlpQG5u8y8TC5CLb6mGmr7Hi QrjbZ//CIx8ykX3mrrhsOUAXlPZrljWz/rVdxMMQgthdtmFFLdyYadUF5lZSOGngDZ pyF10aT05VMWfTYj2g6SI0OqnFbg3DMKwVo1saN3SwAdj2oouv76SehoVEuBmoxciZ hFDqjkqpYX6ow== Date: Wed, 21 May 2025 08:26:05 +0900 From: Masami Hiramatsu (Google) To: Namhyung Kim Cc: Steven Rostedt , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, x86@kernel.org, Masami Hiramatsu , Mathieu Desnoyers , Josh Poimboeuf , Peter Zijlstra , Ingo Molnar , Jiri Olsa , Thomas Gleixner , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Andrii Nakryiko Subject: Re: [PATCH v9 00/13] unwind_user: x86: Deferred unwinding infrastructure Message-Id: <20250521082605.b4bd632ef1312778ea51dd71@kernel.org> In-Reply-To: References: <20250513223435.636200356@goodmis.org> <20250514132720.6b16880c@gandalf.local.home> X-Mailer: Sylpheed 3.8.0beta1 (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 On Fri, 16 May 2025 16:39:56 -0700 Namhyung Kim wrote: > Hi Steve, > > On Wed, May 14, 2025 at 01:27:20PM -0400, Steven Rostedt wrote: > > On Tue, 13 May 2025 18:34:35 -0400 > > Steven Rostedt wrote: > > > > > This has modifications in x86 and I would like it to go through the x86 > > > tree. Preferably it can go into this merge window so we can focus on getting > > > perf and ftrace to work on top of this. > > > > I think it may be best for me to remove the two x86 specific patches, and > > rebuild the ftrace work on top of it. For testing, I'll just keep those two > > patches in my tree locally, but then I can get this moving for this merge > > window. > > Maybe I asked this before but I don't remember if I got the answer. :) > How does it handle task exits as it won't go to userspace? I guess it'll > lose user callstacks for exit syscalls and other termination paths. > > Similarly, it will miss user callstacks in the samples at the end of > profiling if the target tasks remain in the kernel (or they sleep). > It looks like a fundamental limitation of the deferred callchains. Can we use a hybrid approach for this case? It might be more balanced (from the performance point of view) to save the full stack in a classic way only in this case, rather than faulting on process exit or doing file access just to load the sframe. Thanks, > > Thanks, > Namhyung > > > > > Next merge window, we can spend more time on getting the perf API working > > properly. > > > > -- Steve -- Masami Hiramatsu (Google)