From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755905AbbAJAen (ORCPT ); Fri, 9 Jan 2015 19:34:43 -0500 Received: from mail-pa0-f52.google.com ([209.85.220.52]:46727 "EHLO mail-pa0-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755269AbbAJAel (ORCPT ); Fri, 9 Jan 2015 19:34:41 -0500 From: John Stultz To: Linux Kernel Mailing List Cc: John Stultz , Dave Jones , Linus Torvalds , Thomas Gleixner , Richard Cochran , Prarit Bhargava , Stephen Boyd , Ingo Molnar , Peter Zijlstra Subject: [PATCH 05/10] time: Add debugging checks to warn if we see delays Date: Fri, 9 Jan 2015 16:34:23 -0800 Message-Id: <1420850068-27828-6-git-send-email-john.stultz@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1420850068-27828-1-git-send-email-john.stultz@linaro.org> References: <1420850068-27828-1-git-send-email-john.stultz@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Recently there's been some request for better sanity checking in the time code, so that its more clear when something is going wrong since timekeeping issues could manifest in a large number of strange ways with various subsystems. Thus, this patch adds some extra infrastructure to add a check update_wall_time to print warnings if we see the call delayed beyond the max_cycles overflow point, or beyond the clocksource max_idle_ns value which is currently 50% of the overflow point. Tested this a bit by halting qemu for specified lengths of time to trigger the warnings. Cc: Dave Jones Cc: Linus Torvalds Cc: Thomas Gleixner Cc: Richard Cochran Cc: Prarit Bhargava Cc: Stephen Boyd Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: John Stultz --- kernel/time/jiffies.c | 1 + kernel/time/timekeeping.c | 18 ++++++++++++++++++ 2 files changed, 19 insertions(+) diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c index a6a5bf5..7e41390 100644 --- a/kernel/time/jiffies.c +++ b/kernel/time/jiffies.c @@ -71,6 +71,7 @@ static struct clocksource clocksource_jiffies = { .mask = 0xffffffff, /*32bits*/ .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */ .shift = JIFFIES_SHIFT, + .max_cycles = 10, }; __cacheline_aligned_in_smp DEFINE_SEQLOCK(jiffies_lock); diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 6a93185..0dcceba 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -1319,6 +1319,22 @@ static int __init timekeeping_init_ops(void) } device_initcall(timekeeping_init_ops); +static void timekeeping_check_offset(struct timekeeper *tk, cycle_t offset) +{ + + cycle_t max_cycles = tk->tkr.clock->max_cycles; + const char *name = tk->tkr.clock->name; + + if (offset > max_cycles) + printk("ERROR: cycle offset (%lld) is larger then" + " allowed %s max_cycles (%lld)\n", + offset, name, max_cycles); + else if (offset > (max_cycles >> 1)) + printk("WARNING: cycle offset (%lld) is past" + " the %s 50%% safety margin (%lld)\n", + offset, name, max_cycles>>1); +} + /* * Apply a multiplier adjustment to the timekeeper */ @@ -1602,6 +1618,8 @@ void update_wall_time(void) if (offset < real_tk->cycle_interval) goto out; + timekeeping_check_offset(real_tk, offset); + /* * With NO_HZ we may have to accumulate many cycle_intervals * (think "ticks") worth of time at once. To do this efficiently, -- 1.9.1