From patchwork Fri Mar 30 15:01:31 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chris Wilson X-Patchwork-Id: 10317815 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id E752560467 for ; Fri, 30 Mar 2018 15:01:50 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id D81BD2A5BC for ; Fri, 30 Mar 2018 15:01:50 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id CCFA02A5CB; Fri, 30 Mar 2018 15:01:50 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher DHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 3FC472A5BC for ; Fri, 30 Mar 2018 15:01:49 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 2A8206E40B; Fri, 30 Mar 2018 15:01:49 +0000 (UTC) X-Original-To: intel-gfx@lists.freedesktop.org Delivered-To: intel-gfx@lists.freedesktop.org Received: from fireflyinternet.com (mail.fireflyinternet.com [109.228.58.192]) by gabe.freedesktop.org (Postfix) with ESMTPS id A2C3E6E8E0 for ; Fri, 30 Mar 2018 15:01:46 +0000 (UTC) X-Default-Received-SPF: pass (skip=forwardok (res=PASS)) x-ip-name=78.156.65.138; Received: from haswell.alporthouse.com (unverified [78.156.65.138]) by fireflyinternet.com (Firefly Internet (M1)) with ESMTP id 11216169-1500050 for multiple; Fri, 30 Mar 2018 16:01:35 +0100 Received: by haswell.alporthouse.com (sSMTP sendmail emulation); Fri, 30 Mar 2018 16:01:34 +0100 From: Chris Wilson To: linux-kernel@vger.kernel.org Date: Fri, 30 Mar 2018 16:01:31 +0100 Message-Id: <20180330150132.16903-1-chris@chris-wilson.co.uk> X-Mailer: git-send-email 2.16.3 X-Originating-IP: 78.156.65.138 X-Country: code=GB country="United Kingdom" ip=78.156.65.138 Subject: [Intel-gfx] [PATCH v2 1/2] trace: Default to using trace_global_clock if sched_clock is unstable X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: intel-gfx@lists.freedesktop.org, Steven Rostedt MIME-Version: 1.0 Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" X-Virus-Scanned: ClamAV using ClamSMTP Across suspend, we may see a very large drift in timestamps if the sched clock is unstable, prompting the global trace's ringbuffer code to warn and suggest switching to the global clock. Preempt this request by detecting when the sched clock is unstable (determined during late_initcall) and automatically switching the default clock over to trace_global_clock. This should prevent requiring user interaction to resolve warnings such as: Delta way too big! 18446743856563626466 ts=18446744054496180323 write stamp = 197932553857 If you just came from a suspend/resume, please switch to the trace global clock: echo global > /sys/kernel/debug/tracing/trace_clock Signed-off-by: Chris Wilson Cc: Steven Rostedt (VMware) --- v2: Tell the user what's happening and what they can do to correct it. --- kernel/trace/trace.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 13baf85b27d8..7c155fa879e1 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -41,6 +41,7 @@ #include #include #include +#include #include #include "trace.h" @@ -8505,3 +8506,21 @@ __init static int clear_boot_tracer(void) fs_initcall(tracer_init_tracefs); late_initcall_sync(clear_boot_tracer); + +#ifdef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK +__init static int tracing_set_default_clock(void) +{ + /* sched_clock_stable() is determined in late_initcall */ + if (trace_boot_clock || sched_clock_stable()) { + printk(KERN_WARNING + "Unstable clock detected, switching default tracing clock to \"global\"\n" + "If you want to keep using the local clock, then add:\n" + " \"trace_clock=local\"\n" + "on the kernel command line\n"); + tracing_set_clock(&global_trace, "global"); + } + + return 0; +} +late_initcall_sync(tracing_set_default_clock); +#endif