linux-kernel - Re: [PATCH v2] Fix hardware IRQ time accounting problem.

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Message-Id: <1196786641.10274.20.camel@johannes.berg>
Date:	Tue, 04 Dec 2007 17:44:01 +0100
From:	Johannes Berg <johannes@...solutions.net>
To:	Tony Breeds <tony@...eyournoodle.com>
Cc:	Paul Mackerras <paulus@...ba.org>,
	LinuxPPC-dev <linuxppc-dev@...abs.org>,
	Linux Kernel ML <linux-kernel@...r.kernel.org>,
	Frederik Himpe <fhimpe@...enet.be>,
	linux-usb-devel@...ts.sourceforge.net
Subject: Re: [PATCH v2] Fix hardware IRQ time accounting problem.


On Tue, 2007-12-04 at 16:51 +1100, Tony Breeds wrote:
> The commit fa13a5a1f25f671d084d8884be96fc48d9b68275 (sched: restore
> deterministic CPU accounting on powerpc), unconditionally calls
> update_process_tick() in system context.  In the deterministic accounting case
> this is the correct thing to do.  However, in the non-deterministic accounting
> case we need to not do this, and results in the time accounted as hardware irq
> time being artificially elevated.

Cool, I wouldn't have stood a chance of tracking this down :) Thanks,
I'll apply it to my testing tree later today.

> Signed-off-by: Tony Breeds <tony@...eyournoodle.com>
> ---
> The problem was seen and reported by Johannes Berg  and Frederik Himpe.
> Paul, I think this is good for 2.6.24.
> 
> Changes since v1:
>  - I noticed that the #define was explictly using "current" rather than
>    the task passed in.  Using tsk is the right thing to do.
>  - The whiteapce changes dirty-up the patch and are un-needed with the
>    change above.
> 
>  arch/powerpc/kernel/process.c |    2 +-
>  include/asm-powerpc/time.h    |    8 ++------
>  2 files changed, 3 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 41e13f4..b9d8837 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -350,7 +350,7 @@ struct task_struct *__switch_to(struct task_struct *prev,
>  	local_irq_save(flags);
>  
>  	account_system_vtime(current);
> -	account_process_tick(current, 0);
> +	account_process_vtime(current);
>  	calculate_steal_time();
>  
>  	last = _switch(old_thread, new_thread);
> diff --git a/include/asm-powerpc/time.h b/include/asm-powerpc/time.h
> index 780f826..a7281e0 100644
> --- a/include/asm-powerpc/time.h
> +++ b/include/asm-powerpc/time.h
> @@ -237,18 +237,14 @@ struct cpu_usage {
>  
>  DECLARE_PER_CPU(struct cpu_usage, cpu_usage_array);
>  
> -#ifdef CONFIG_VIRT_CPU_ACCOUNTING
> -extern void account_process_vtime(struct task_struct *tsk);
> -#else
> -#define account_process_vtime(tsk)		do { } while (0)
> -#endif
> -
>  #if defined(CONFIG_VIRT_CPU_ACCOUNTING)
>  extern void calculate_steal_time(void);
>  extern void snapshot_timebases(void);
> +#define account_process_vtime(tsk)		account_process_tick(tsk, 0);
>  #else
>  #define calculate_steal_time()			do { } while (0)
>  #define snapshot_timebases()			do { } while (0)
> +#define account_process_vtime(tsk)		do { } while (0)
>  #endif
>  
>  extern void secondary_cpu_time_init(void);

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