linux-kernel - Re: [PATCH] Calling check_system_tsc_reliable before unsynchronized

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Date:   Tue, 20 Jun 2017 15:14:26 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Zhenzhong Duan <zhenzhong.duan@...cle.com>
cc:     mingo@...hat.com, hpa@...or.com, x86@...nel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Calling check_system_tsc_reliable before
 unsynchronized_tsc

On Tue, 13 Jun 2017, Zhenzhong Duan wrote:
> 在 2017/6/13 0:03, Thomas Gleixner 写道:
> > On Thu, 8 Jun 2017, Zhenzhong Duan wrote:
> > 
> > > 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, or else this check makes no sense.
> > > 
> > > Though X86_FEATURE_CONSTANT_TSC is usually set for TSC reliable system,
> > > just
> > > in
> > > case.
> > > 
> > > Signed-off-by: Zhenzhong Duan <zhenzhong.duan@...cle.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();
> > > -
> > What kind of patch is that? Definitely nothing which can be applied.
> To avoid using unassigned variable tsc_clocksource_reliable.
> Or what's the purpose of if (tsc_clocksource_reliable) check in
> unsynchronized_tsc()?

That's not the question. The patch format itself is broken:

@@ -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();
-

That is not a patch created with diff -u or any other mechanism
which creates properly formatted patches.

Thanks,

	tglx