Re: [PATCH] sched: account system time properly

[Andrew Gallatin <gallatin@myri.com>]

Eric Dumazet wrote:

> On mostly idle cpu, irqs were thus not accounted and top or mpstat could tell
> user/admin that cpu was 100 % idle, 0.00 % irq, 0.00 % softirq, while it was not.
> 
> Reported-by: Andrew Gallatin <gallatin@myri.com>
> Re-reported-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
> Tested-by: Eric Dumazet <dada1@cosmosbay.com>
> Acked-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
> 
> diff --git a/kernel/sched.c b/kernel/sched.c
> index b902e58..26efa47 100644
> --- a/kernel/sched.c
> +++ b/kernel/sched.c
> @@ -4732,7 +4732,7 @@ void account_process_tick(struct task_struct *p, int user_tick)
>  
>  	if (user_tick)
>  		account_user_time(p, one_jiffy, one_jiffy_scaled);
> -	else if (p != rq->idle)
> +	else if ((p != rq->idle) || (irq_count() != HARDIRQ_OFFSET))
>  		account_system_time(p, HARDIRQ_OFFSET, one_jiffy,
>  				    one_jiffy_scaled);
>  	else
> 

I can confirm this fixes the issue for me.   Thank you, and I am
sorry if my git-bisect fumble-fingers caused too much wasted time.

Cheers,

Drew