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authorTom Hromatka <tom.hromatka@oracle.com>2017-01-04 15:28:04 -0700
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2018-03-22 09:17:42 +0100
commit00c001fbdad55884d4316f528ffc6a0017ca88dd (patch)
tree71e6cef74e40a74e125f525f7b0b1de961598dcf /kernel
parentae0258a81896f9a26b1a84102fe71dd71662b727 (diff)
sysrq: Reset the watchdog timers while displaying high-resolution timers
[ Upstream commit 0107042768658fea9f5f5a9c00b1c90f5dab6a06 ] On systems with a large number of CPUs, running sysrq-<q> can cause watchdog timeouts. There are two slow sections of code in the sysrq-<q> path in timer_list.c. 1. print_active_timers() - This function is called by print_cpu() and contains a slow goto loop. On a machine with hundreds of CPUs, this loop took approximately 100ms for the first CPU in a NUMA node. (Subsequent CPUs in the same node ran much quicker.) The total time to print all of the CPUs is ultimately long enough to trigger the soft lockup watchdog. 2. print_tickdevice() - This function outputs a large amount of textual information. This function also took approximately 100ms per CPU. Since sysrq-<q> is not a performance critical path, there should be no harm in touching the nmi watchdog in both slow sections above. Touching it in just one location was insufficient on systems with hundreds of CPUs as occasional timeouts were still observed during testing. This issue was observed on an Oracle T7 machine with 128 CPUs, but I anticipate it may affect other systems with similarly large numbers of CPUs. Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com> Reviewed-by: Rob Gardner <rob.gardner@oracle.com> Signed-off-by: John Stultz <john.stultz@linaro.org> Signed-off-by: Sasha Levin <alexander.levin@microsoft.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/time/timer_list.c6
1 files changed, 6 insertions, 0 deletions
diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
index ba7d8b288bb3..ef4f16e81283 100644
--- a/kernel/time/timer_list.c
+++ b/kernel/time/timer_list.c
@@ -16,6 +16,7 @@
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/kallsyms.h>
+#include <linux/nmi.h>
#include <asm/uaccess.h>
@@ -96,6 +97,9 @@ print_active_timers(struct seq_file *m, struct hrtimer_clock_base *base,
next_one:
i = 0;
+
+ touch_nmi_watchdog();
+
raw_spin_lock_irqsave(&base->cpu_base->lock, flags);
curr = timerqueue_getnext(&base->active);
@@ -207,6 +211,8 @@ print_tickdevice(struct seq_file *m, struct tick_device *td, int cpu)
{
struct clock_event_device *dev = td->evtdev;
+ touch_nmi_watchdog();
+
SEQ_printf(m, "Tick Device: mode: %d\n", td->mode);
if (cpu < 0)
SEQ_printf(m, "Broadcast device\n");