* [RFC PATCH RT] x86/tsc: Add option to disable tsc clocksource watchdog
@ 2019-03-07 12:09 Juri Lelli
2019-03-14 7:09 ` Juri Lelli
2019-03-22 13:19 ` [tip:x86/timers] " tip-bot for Juri Lelli
0 siblings, 2 replies; 4+ messages in thread
From: Juri Lelli @ 2019-03-07 12:09 UTC (permalink / raw)
To: tglx, bigeasy
Cc: linux-rt-users, peterz, linux-kernel, bristot, williams, Juri Lelli
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@redhat.com>
---
Sending this out as an RFC after yesterday discussion with Thomas on IRC.
AFAICT, CLOCK_SOURCE_MUST_VERIFY only controls enqueue\dequeue of the
watchdog. TSC sync checks are still done if tsc_clocksource_reliable is
set (booting w/o tsc=reliable).
Thomas, is this anywhere close to what you had in mind?
---
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 f5acf35c712f..ea7c4967aa80 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4619,6 +4619,10 @@
[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 6d5dc5dabfd7..4b753d057aee 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;
}
@@ -1347,7 +1350,7 @@ 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))
--
2.17.2
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [RFC PATCH RT] x86/tsc: Add option to disable tsc clocksource watchdog
2019-03-07 12:09 [RFC PATCH RT] x86/tsc: Add option to disable tsc clocksource watchdog Juri Lelli
@ 2019-03-14 7:09 ` Juri Lelli
2019-03-20 11:51 ` Sebastian Andrzej Siewior
2019-03-22 13:19 ` [tip:x86/timers] " tip-bot for Juri Lelli
1 sibling, 1 reply; 4+ messages in thread
From: Juri Lelli @ 2019-03-14 7:09 UTC (permalink / raw)
To: tglx, bigeasy; +Cc: linux-rt-users, peterz, linux-kernel, bristot, williams
Hi,
On 07/03/19 13:09, Juri Lelli wrote:
> 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.
Gentle ping.
Does this make any sense?
Thanks,
- Juri
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [RFC PATCH RT] x86/tsc: Add option to disable tsc clocksource watchdog
2019-03-14 7:09 ` Juri Lelli
@ 2019-03-20 11:51 ` Sebastian Andrzej Siewior
0 siblings, 0 replies; 4+ messages in thread
From: Sebastian Andrzej Siewior @ 2019-03-20 11:51 UTC (permalink / raw)
To: Juri Lelli; +Cc: tglx, linux-rt-users, peterz, linux-kernel, bristot, williams
On 2019-03-14 08:09:51 [+0100], Juri Lelli wrote:
> Hi,
>
> On 07/03/19 13:09, Juri Lelli wrote:
> > 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.
>
> Gentle ping.
>
> Does this make any sense?
I have to reroute this ping to tglx since I wasn't involved.
> Thanks,
>
> - Juri
Sebastian
^ permalink raw reply [flat|nested] 4+ messages in thread
* [tip:x86/timers] x86/tsc: Add option to disable tsc clocksource watchdog
2019-03-07 12:09 [RFC PATCH RT] x86/tsc: Add option to disable tsc clocksource watchdog Juri Lelli
2019-03-14 7:09 ` Juri Lelli
@ 2019-03-22 13:19 ` tip-bot for Juri Lelli
1 sibling, 0 replies; 4+ messages in thread
From: tip-bot for Juri Lelli @ 2019-03-22 13:19 UTC (permalink / raw)
To: linux-tip-commits; +Cc: mingo, linux-kernel, juri.lelli, hpa, tglx
Commit-ID: 0f0b7e1cc7abf8e1a8b301f2868379d611d05ae2
Gitweb: https://git.kernel.org/tip/0f0b7e1cc7abf8e1a8b301f2868379d611d05ae2
Author: Juri Lelli <juri.lelli@redhat.com>
AuthorDate: Thu, 7 Mar 2019 13:09:13 +0100
Committer: Thomas Gleixner <tglx@linutronix.de>
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@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: bigeasy@linutronix.de
Cc: linux-rt-users@vger.kernel.org
Cc: peterz@infradead.org
Cc: bristot@redhat.com
Cc: williams@redhat.com
Link: https://lkml.kernel.org/r/20190307120913.13168-1-juri.lelli@redhat.com
---
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))
^ permalink raw reply related [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-03-22 13:19 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2019-03-07 12:09 [RFC PATCH RT] x86/tsc: Add option to disable tsc clocksource watchdog Juri Lelli
2019-03-14 7:09 ` Juri Lelli
2019-03-20 11:51 ` Sebastian Andrzej Siewior
2019-03-22 13:19 ` [tip:x86/timers] " tip-bot for Juri Lelli
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