From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 2E3A6C61DA4 for ; Mon, 6 Feb 2023 09:56:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229819AbjBFJ4f (ORCPT ); Mon, 6 Feb 2023 04:56:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49946 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229522AbjBFJ4c (ORCPT ); Mon, 6 Feb 2023 04:56:32 -0500 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id C9C8A1CADB for ; Mon, 6 Feb 2023 01:56:31 -0800 (PST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CD3F1113E; Mon, 6 Feb 2023 01:57:13 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.91.13]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id CB16D3F71E; Mon, 6 Feb 2023 01:56:28 -0800 (PST) Date: Mon, 6 Feb 2023 09:56:26 +0000 From: Mark Rutland To: Guo Ren Cc: Evgenii Shatokhin , suagrfillet@gmail.com, andy.chiu@sifive.com, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, Guo Ren , anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, conor.dooley@microchip.com, heiko@sntech.de, rostedt@goodmis.org, mhiramat@kernel.org, jolsa@redhat.com, bp@suse.de, jpoimboe@kernel.org, linux@yadro.com Subject: Re: [PATCH -next V7 0/7] riscv: Optimize function trace Message-ID: References: <20230112090603.1295340-1-guoren@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Feb 04, 2023 at 02:40:52PM +0800, Guo Ren wrote: > On Mon, Jan 16, 2023 at 11:02 PM Evgenii Shatokhin > wrote: > > > > Hi, > > > > On 12.01.2023 12:05, guoren@kernel.org wrote: > > > From: Guo Ren > > > > > > The previous ftrace detour implementation fc76b8b8011 ("riscv: Using > > > PATCHABLE_FUNCTION_ENTRY instead of MCOUNT") contain three problems. > > > > > > - The most horrible bug is preemption panic which found by Andy [1]. > > > Let's disable preemption for ftrace first, and Andy could continue > > > the ftrace preemption work. > > > > It seems, the patches #2-#7 of this series do not require "riscv: > > ftrace: Fixup panic by disabling preemption" and can be used without it. > > > > How about moving that patch out of the series and processing it separately? > Okay. > > > > > As it was pointed out in the discussion of that patch, some other > > solution to non-atomic changes of the prologue might be needed anyway. > I think you mean Mark Rutland's DYNAMIC_FTRACE_WITH_CALL_OPS. But that > still needs to be ready. Let's disable PREEMPT for ftrace first. FWIW, taking the patch to disable FTRACE with PREEMPT for now makes sense to me, too. The DYNAMIC_FTRACE_WITH_CALL_OPS patches should be in v6.3. They're currently queued in the arm64 tree in the for-next/ftrace branch: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-next/ftrace https://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git/ ... and those *should* be in v6.3. Patches to imeplement DIRECT_CALLS atop that are in review at the moment: https://lore.kernel.org/linux-arm-kernel/20230201163420.1579014-1-revest@chromium.org/ ... and if riscv uses the CALL_OPS approach, I believe it can do much the same there. If riscv wants to do a single atomic patch to each patch-site (to avoid stop_machine()), then direct calls would always needs to bounce through the ftrace_caller trampoline (and acquire the direct call from the ftrace_ops), but that might not be as bad as it sounds -- from benchmarking on arm64, the bulk of the overhead seen with direct calls is when using the list_ops or having to do a hash lookup, and both of those are avoided with the CALL_OPS approach. Calling directly from the patch-site is a minor optimization relative to skipping that work. Thanks, Mark.