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 X-Spam-Level: X-Spam-Status: No, score=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1E13DC04EBF for ; Wed, 5 Dec 2018 09:54:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E203920989 for ; Wed, 5 Dec 2018 09:54:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E203920989 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730147AbeLEJyf (ORCPT ); Wed, 5 Dec 2018 04:54:35 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:50250 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730127AbeLEJy0 (ORCPT ); Wed, 5 Dec 2018 04:54:26 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 276EC80D; Wed, 5 Dec 2018 01:54:26 -0800 (PST) Received: from edgewater-inn.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id EB5443F575; Wed, 5 Dec 2018 01:54:25 -0800 (PST) Received: by edgewater-inn.cambridge.arm.com (Postfix, from userid 1000) id 974C51AE0BA8; Wed, 5 Dec 2018 09:54:46 +0000 (GMT) Date: Wed, 5 Dec 2018 09:54:46 +0000 From: Will Deacon To: Anders Roxell Cc: rostedt@goodmis.org, mingo@redhat.com, catalin.marinas@arm.com, keescook@chromium.org, arnd@arndb.de, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH v2] tracing: add cond_resched to ftrace_replace_code() Message-ID: <20181205095445.GA14317@arm.com> References: <20181204192903.8193-1-anders.roxell@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181204192903.8193-1-anders.roxell@linaro.org> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Anders, Steve, On Tue, Dec 04, 2018 at 08:29:03PM +0100, Anders Roxell wrote: > When running in qemu on an kernel built with allmodconfig and debug > options (in particular kcov and ubsan) enabled, ftrace_replace_code > function call take minutes. The ftrace selftest calls > ftrace_replace_code to look >40000 through > ftrace_make_call/ftrace_make_nop, and these end up calling > __aarch64_insn_write/aarch64_insn_patch_text_nosync. > > Microseconds add up because this is called in a loop for each dyn_ftrace > record, and this triggers the softlockup watchdog unless we let it sleep > occasionally. > > Rework so that we call cond_resched() if !irqs_disabled() && !preempt_count(). > > Suggested-by: Steven Rostedt (VMware) > Signed-off-by: Anders Roxell > --- > kernel/trace/ftrace.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > index c375e33239f7..7080eb464983 100644 > --- a/kernel/trace/ftrace.c > +++ b/kernel/trace/ftrace.c > @@ -2419,11 +2419,19 @@ void __weak ftrace_replace_code(int enable) > { > struct dyn_ftrace *rec; > struct ftrace_page *pg; > + bool schedulable; > int failed; > > if (unlikely(ftrace_disabled)) > return; > > + /* > + * Some archs calls this function with interrupts or preemption > + * disabled. However, for other archs that can preempt, this can cause > + * an tremendous unneeded latency. > + */ > + schedulable = !irqs_disabled() && !preempt_count(); Is there a reason not to use preemptible() here? Will