Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

[Quan Xu]

On 2017/9/1 14:49, Quan Xu wrote:

on 2017/8/29 22:39, Borislav Petkov wrote:

On Tue, Aug 29, 2017 at 11:46:37AM +, Yang Zhang wrote:

Add poll in do_idle. For UP VM, if there are running task, it will not
goes into idle path, so we only enable poll in SMP VM.

Signed-off-by: Yang Zhang 
Signed-off-by: Quan Xu 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: "H. Peter Anvin" 
Cc: x...@kernel.org
Cc: Peter Zijlstra 
Cc: Borislav Petkov 
Cc: Kyle Huey 
Cc: Andy Lutomirski 
Cc: Len Brown 
Cc: linux-ker...@vger.kernel.org
---
  arch/x86/kernel/process.c | 7 +++
  kernel/sched/idle.c   | 2 ++
  2 files changed, 9 insertions(+)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 3ca1980..def4113 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -332,6 +332,13 @@ void arch_cpu_idle(void)
  x86_idle();
  }
  +#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT)
+void arch_cpu_idle_poll(void)
+{
+    paravirt_idle_poll();
+}
+#endif

So this will get called on any system which has CONFIG_PARAVIRT enabled
*even* if they're not running any guests.

Huh?

 Borislav,
 think twice, it is better to run ander an IF condition, to make 
sure they are running any guests.


  Quan

Borislav ,
   yes, this will get called on any system which has CONFIG_PARAVIRT 
enabled.


   but if they are not running any guests,  the callback is 
paravirt_nop() ,
   IIUC which is as similar as the other paravirt_*, such as 
paravirt_pgd_free()..


 - Quan


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Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

[Borislav Petkov]

On Thu, Sep 14, 2017 at 04:41:39PM +0800, Quan Xu wrote:
> > > On Tue, Aug 29, 2017 at 11:46:37AM +, Yang Zhang wrote:
> > > > Add poll in do_idle. For UP VM, if there are running task, it will not
> > > > goes into idle path, so we only enable poll in SMP VM.
> > > > 
> > > > Signed-off-by: Yang Zhang 
> > > > Signed-off-by: Quan Xu 
> > > Broken SoB chain.
> >   Peter,  I can't follow 'Broken SoB chain'.. could you explain more
> > about it?
> > 
>     Peter, Ping..

The SOB chain needs to show the path from the author to the upstream
maintainer. Yours has Yang before you, which doesn't say what his role
is.

Read Documentation/process/submitting-patches.rst, section 11.

-- 
Regards/Gruss,
Boris.

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Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

[Quan Xu]

on 2017/9/1 13:57, Quan Xu wrote:

on 2017/8/29 20:45, Peter Zijlstra wrote:


On Tue, Aug 29, 2017 at 11:46:37AM +, Yang Zhang wrote:

Add poll in do_idle. For UP VM, if there are running task, it will not
goes into idle path, so we only enable poll in SMP VM.

Signed-off-by: Yang Zhang 
Signed-off-by: Quan Xu 

Broken SoB chain.
  Peter,  I can't follow 'Broken SoB chain'.. could you explain more 
about it?



    Peter, Ping..

Quan




  -Quan


diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 6c23e30..b374744 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -74,6 +74,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
  }
    /* Weak implementations for optional arch specific functions */
+void __weak arch_cpu_idle_poll(void) { }
  void __weak arch_cpu_idle_prepare(void) { }
  void __weak arch_cpu_idle_enter(void) { }

And not a word on why we need a new arch hook. What's wrong with
arch_cpu_idle_enter() for instance?




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Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

[Quan Xu]

on 2017/8/29 22:39, Borislav Petkov wrote:

On Tue, Aug 29, 2017 at 11:46:37AM +, Yang Zhang wrote:

Add poll in do_idle. For UP VM, if there are running task, it will not
goes into idle path, so we only enable poll in SMP VM.

Signed-off-by: Yang Zhang 
Signed-off-by: Quan Xu 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: "H. Peter Anvin" 
Cc: x...@kernel.org
Cc: Peter Zijlstra 
Cc: Borislav Petkov 
Cc: Kyle Huey 
Cc: Andy Lutomirski 
Cc: Len Brown 
Cc: linux-ker...@vger.kernel.org
---
  arch/x86/kernel/process.c | 7 +++
  kernel/sched/idle.c   | 2 ++
  2 files changed, 9 insertions(+)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 3ca1980..def4113 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -332,6 +332,13 @@ void arch_cpu_idle(void)
x86_idle();
  }
  
+#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT)

+void arch_cpu_idle_poll(void)
+{
+   paravirt_idle_poll();
+}
+#endif

So this will get called on any system which has CONFIG_PARAVIRT enabled
*even* if they're not running any guests.

Huh?

   Borislav ,
   yes,  this will get called on any system which has CONFIG_PARAVIRT 
enabled.


   but if they are not running any guests,  the callback is 
paravirt_nop() ,
   IIUC which is as similar as the other paravirt_*, such as 
paravirt_pgd_free()..


 - Quan
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Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

[Quan Xu]

on 2017/8/29 20:45, Peter Zijlstra wrote:


On Tue, Aug 29, 2017 at 11:46:37AM +, Yang Zhang wrote:

Add poll in do_idle. For UP VM, if there are running task, it will not
goes into idle path, so we only enable poll in SMP VM.

Signed-off-by: Yang Zhang 
Signed-off-by: Quan Xu 

Broken SoB chain.

  Peter,  I can't follow 'Broken SoB chain'.. could you more about it?

  -Quan


diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 6c23e30..b374744 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -74,6 +74,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
  }
  
  /* Weak implementations for optional arch specific functions */

+void __weak arch_cpu_idle_poll(void) { }
  void __weak arch_cpu_idle_prepare(void) { }
  void __weak arch_cpu_idle_enter(void) { }

And not a word on why we need a new arch hook. What's wrong with
arch_cpu_idle_enter() for instance?


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Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

[Borislav Petkov]

On Tue, Aug 29, 2017 at 11:46:37AM +, Yang Zhang wrote:
> Add poll in do_idle. For UP VM, if there are running task, it will not
> goes into idle path, so we only enable poll in SMP VM.
> 
> Signed-off-by: Yang Zhang 
> Signed-off-by: Quan Xu 
> Cc: Thomas Gleixner 
> Cc: Ingo Molnar 
> Cc: "H. Peter Anvin" 
> Cc: x...@kernel.org
> Cc: Peter Zijlstra 
> Cc: Borislav Petkov 
> Cc: Kyle Huey 
> Cc: Andy Lutomirski 
> Cc: Len Brown 
> Cc: linux-ker...@vger.kernel.org
> ---
>  arch/x86/kernel/process.c | 7 +++
>  kernel/sched/idle.c   | 2 ++
>  2 files changed, 9 insertions(+)
> 
> diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
> index 3ca1980..def4113 100644
> --- a/arch/x86/kernel/process.c
> +++ b/arch/x86/kernel/process.c
> @@ -332,6 +332,13 @@ void arch_cpu_idle(void)
>   x86_idle();
>  }
>  
> +#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT)
> +void arch_cpu_idle_poll(void)
> +{
> + paravirt_idle_poll();
> +}
> +#endif

So this will get called on any system which has CONFIG_PARAVIRT enabled
*even* if they're not running any guests.

Huh?

-- 
Regards/Gruss,
Boris.

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Re: [RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

[Peter Zijlstra]

On Tue, Aug 29, 2017 at 11:46:37AM +, Yang Zhang wrote:
> Add poll in do_idle. For UP VM, if there are running task, it will not
> goes into idle path, so we only enable poll in SMP VM.
> 
> Signed-off-by: Yang Zhang 
> Signed-off-by: Quan Xu 

Broken SoB chain.

> diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
> index 6c23e30..b374744 100644
> --- a/kernel/sched/idle.c
> +++ b/kernel/sched/idle.c
> @@ -74,6 +74,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
>  }
>  
>  /* Weak implementations for optional arch specific functions */
> +void __weak arch_cpu_idle_poll(void) { }
>  void __weak arch_cpu_idle_prepare(void) { }
>  void __weak arch_cpu_idle_enter(void) { }

And not a word on why we need a new arch hook. What's wrong with
arch_cpu_idle_enter() for instance?
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[RFC PATCH v2 3/7] sched/idle: Add poll before enter real idle path

[Yang Zhang]

Add poll in do_idle. For UP VM, if there are running task, it will not
goes into idle path, so we only enable poll in SMP VM.

Signed-off-by: Yang Zhang 
Signed-off-by: Quan Xu 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: "H. Peter Anvin" 
Cc: x...@kernel.org
Cc: Peter Zijlstra 
Cc: Borislav Petkov 
Cc: Kyle Huey 
Cc: Andy Lutomirski 
Cc: Len Brown 
Cc: linux-ker...@vger.kernel.org
---
 arch/x86/kernel/process.c | 7 +++
 kernel/sched/idle.c   | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 3ca1980..def4113 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -332,6 +332,13 @@ void arch_cpu_idle(void)
x86_idle();
 }
 
+#if defined(CONFIG_SMP) && defined(CONFIG_PARAVIRT)
+void arch_cpu_idle_poll(void)
+{
+   paravirt_idle_poll();
+}
+#endif
+
 /*
  * We use this if we don't have any better idle routine..
  */
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 6c23e30..b374744 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -74,6 +74,7 @@ static noinline int __cpuidle cpu_idle_poll(void)
 }
 
 /* Weak implementations for optional arch specific functions */
+void __weak arch_cpu_idle_poll(void) { }
 void __weak arch_cpu_idle_prepare(void) { }
 void __weak arch_cpu_idle_enter(void) { }
 void __weak arch_cpu_idle_exit(void) { }
@@ -219,6 +220,7 @@ static void do_idle(void)
 */
 
__current_set_polling();
+   arch_cpu_idle_poll();
quiet_vmstat();
tick_nohz_idle_enter();
 
-- 
1.8.3.1

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