[PATCH RESEND] Calling check_system_tsc_reliable() before unsynchronized_tsc()

[PATCH RESEND] Calling check_system_tsc_reliable() before unsynchronized_tsc()

[Zhenzhong Duan]

unsynchronized_tsc() checks value of tsc_clocksource_reliable which is set by
check_system_tsc_reliable(). It's better to move check_system_tsc_reliable() at
front.

Though X86_FEATURE_CONSTANT_TSC is usually set for TSC reliable system, just in
case.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
---
 arch/x86/kernel/tsc.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 714dfba..a316bdd 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1412,11 +1412,11 @@ void __init tsc_init(void)
 
 	use_tsc_delay();
 
+	check_system_tsc_reliable();
+
 	if (unsynchronized_tsc())
 		mark_tsc_unstable("TSCs unsynchronized");
 
-	check_system_tsc_reliable();
-
 	detect_art();
 }
 
-- 
1.7.3

Re: [PATCH RESEND] Calling check_system_tsc_reliable() before unsynchronized_tsc()

[Thomas Gleixner]

Zhenzhong,

On Wed, 21 Jun 2017, Zhenzhong Duan wrote:

So the patch format is now correct, but the subject line is missing a
proper subsystem prefix. Please use 'git log 'path/to/patched/file' next
time to see what the usually used prefix for a file is.

In this case it's:   x86/tsc

Also please do not use [PATCH RESEND] when your patch is different from the
version you sent before. Please use [PATCH v2] instead.

> unsynchronized_tsc() checks value of tsc_clocksource_reliable which is set by
> check_system_tsc_reliable(). It's better to move check_system_tsc_reliable() at
> front.

Please make your statements affirmative. 'It's better' is a weak expression.

> Though X86_FEATURE_CONSTANT_TSC is usually set for TSC reliable system, just in
> case.

So what you wanted to say here is:

   tsc_clocksource_reliable is initialized in check_system_tsc_reliable(),
   but it is checked in unsynchronized_tsc() which is called before the
   initialization.

   In practice that's not an issue because systems which mark the TSC
   reliable have X86_FEATURE_CONSTANT_TSC set as well, which is evaluated
   in unsynchronized_tsc() before tsc_clocksource_reliable.

   Reorder the calls so initialization happens before usage.

All this information is also documented in Documentation/process/.

No need to resend. I'll fix it up for you this time. 
 
Thanks,

	tglx

[tip:x86/timers] x86/tsc: Call check_system_tsc_reliable() before unsynchronized_tsc()

[tip-bot for Zhenzhong Duan]

Commit-ID:  a1272dd5531b259bf7313ac7597a67362698038c
Gitweb:     http://git.kernel.org/tip/a1272dd5531b259bf7313ac7597a67362698038c
Author:     Zhenzhong Duan <zhenzhong.duan@oracle.com>
AuthorDate: Wed, 21 Jun 2017 01:23:37 -0700
Committer:  Thomas Gleixner <tglx@linutronix.de>
CommitDate: Thu, 22 Jun 2017 16:00:03 +0200

x86/tsc: Call check_system_tsc_reliable() before unsynchronized_tsc()

tsc_clocksource_reliable is initialized in check_system_tsc_reliable(), but
it is checked in unsynchronized_tsc() which is called before the
initialization.

In practice that's not an issue because systems which mark the TSC
reliable have X86_FEATURE_CONSTANT_TSC set as well, which is evaluated
in unsynchronized_tsc() before tsc_clocksource_reliable.

Reorder the calls so initialization happens before usage.

[ tglx: Massaged changelog ]

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/b1532ef7-cd9f-45f7-9f49-48dd2a5c2495@default
---
 arch/x86/kernel/tsc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
index 714dfba..a316bdd 100644
--- a/arch/x86/kernel/tsc.c
+++ b/arch/x86/kernel/tsc.c
@@ -1412,11 +1412,11 @@ void __init tsc_init(void)
 
 	use_tsc_delay();
 
+	check_system_tsc_reliable();
+
 	if (unsynchronized_tsc())
 		mark_tsc_unstable("TSCs unsynchronized");
 
-	check_system_tsc_reliable();
-
 	detect_art();
 }
 

Re: [PATCH RESEND] Calling check_system_tsc_reliable() before unsynchronized_tsc()

[Zhenzhong Duan]

在 2017/6/22 21:56, Thomas Gleixner 写道:
> Zhenzhong,
>
> On Wed, 21 Jun 2017, Zhenzhong Duan wrote:
>
> So the patch format is now correct, but the subject line is missing a
> proper subsystem prefix. Please use 'git log 'path/to/patched/file' next
> time to see what the usually used prefix for a file is.
>
> In this case it's:   x86/tsc
>
> Also please do not use [PATCH RESEND] when your patch is different from the
> version you sent before. Please use [PATCH v2] instead.
Got it.
>
>> unsynchronized_tsc() checks value of tsc_clocksource_reliable which is set by
>> check_system_tsc_reliable(). It's better to move check_system_tsc_reliable() at
>> front.
> Please make your statements affirmative. 'It's better' is a weak expression.
>
>> Though X86_FEATURE_CONSTANT_TSC is usually set for TSC reliable system, just in
>> case.
> So what you wanted to say here is:
>
>     tsc_clocksource_reliable is initialized in check_system_tsc_reliable(),
>     but it is checked in unsynchronized_tsc() which is called before the
>     initialization.
>
>     In practice that's not an issue because systems which mark the TSC
>     reliable have X86_FEATURE_CONSTANT_TSC set as well, which is evaluated
>     in unsynchronized_tsc() before tsc_clocksource_reliable.
>
>     Reorder the calls so initialization happens before usage.
Exactly.
>
> All this information is also documented in Documentation/process/.
I'll read them.
>
> No need to resend. I'll fix it up for you this time.
Ok, thanks.

zduan