Commit-ID: 0f0b7e1cc7abf8e1a8b301f2868379d611d05ae2
Gitweb: https://git.kernel.org/tip/0f0b7e1cc7abf8e1a8b301f2868379d611d05ae2
Author: Juri Lelli <juri.lelli@xxxxxxxxxx>
AuthorDate: Thu, 7 Mar 2019 13:09:13 +0100
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 22 Mar 2019 14:14:58 +0100
x86/tsc: Add option to disable tsc clocksource watchdog
Clocksource watchdog has been found responsible for generating latency
spikes (in the 10-20 us range) when woken up to check for TSC stability.
Add an option to disable it at boot.
Signed-off-by: Juri Lelli <juri.lelli@xxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: bigeasy@xxxxxxxxxxxxx
Cc: linux-rt-users@xxxxxxxxxxxxxxx
Cc: peterz@xxxxxxxxxxxxx
Cc: bristot@xxxxxxxxxx
Cc: williams@xxxxxxxxxx
Link: https://lkml.kernel.org/r/20190307120913.13168-1-juri.lelli@xxxxxxxxxx
---
Documentation/admin-guide/kernel-parameters.txt | 4 ++++
arch/x86/kernel/tsc.c | 5 ++++-
2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 2b8ee90bb644..c4d830003b21 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4703,6 +4703,10 @@
[x86] unstable: mark the TSC clocksource as unstable, this
marks the TSC unconditionally unstable at bootup and
avoids any further wobbles once the TSC watchdog notices.
+ [x86] nowatchdog: disable clocksource watchdog. Used
+ in situations with strict latency requirements (where
+ interruptions from clocksource watchdog are not
+ acceptable).
turbografx.map[2|3]= [HW,JOY]
TurboGraFX parallel port interface
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 3fae23834069..aab0c82e0a0d 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -283,6 +283,7 @@ int __init notsc_setup(char *str)
__setup("notsc", notsc_setup);
static int no_sched_irq_time;
+static int no_tsc_watchdog;
static int __init tsc_setup(char *str)
{
@@ -292,6 +293,8 @@ static int __init tsc_setup(char *str)
no_sched_irq_time = 1;
if (!strcmp(str, "unstable"))
mark_tsc_unstable("boot parameter");
+ if (!strcmp(str, "nowatchdog"))
+ no_tsc_watchdog = 1;
return 1;
}
@@ -1349,7 +1352,7 @@ static int __init init_tsc_clocksource(void)
if (tsc_unstable)
goto unreg;
- if (tsc_clocksource_reliable)
+ if (tsc_clocksource_reliable || no_tsc_watchdog)
clocksource_tsc.flags &= ~CLOCK_SOURCE_MUST_VERIFY;
if (boot_cpu_has(X86_FEATURE_NONSTOP_TSC_S3))
|