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Subject: Re: [PATCH] cpufreq: ondemand ignore_nice_level
From: Peter Zijlstra <peterz@infradead.org>
To: joni@shade-fx.com
Cc: linux-kernel@vger.kernel.org, Dave Jones <davej@redhat.com>,
        "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>
Date: Tue, 09 Aug 2011 12:12:39 +0200
In-Reply-To: <4e403bd4.5YAAoSWMDWtU5KOP%joni@shade-fx.com>
References: <4e403bd4.5YAAoSWMDWtU5KOP%joni@shade-fx.com>
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How very good of you to CC all the relevant maintainers..

On Mon, 2011-08-08 at 22:41 +0300, joni@shade-fx.com wrote:
> @@ -3755,7 +3755,7 @@ unsigned long long thread_group_sched_runtime(struct task_struct *p)
>   * @cputime_scaled: cputime scaled by cpu frequency
>   */
>  void account_user_time(struct task_struct *p, cputime_t cputime,
> -                      cputime_t cputime_scaled)
> +               cputime_t cputime_scaled)
>  {
>         struct cpu_usage_stat *cpustat = &kstat_this_cpu.cpustat;
>         cputime64_t tmp;

I'm very sure the old alignment was preferred.

> @@ -3769,9 +3769,11 @@ void account_user_time(struct task_struct *p, cputime_t cputime,
>         tmp = cputime_to_cputime64(cputime);
>         if (TASK_NICE(p) > 0)
>                 cpustat->nice = cputime64_add(cpustat->nice, tmp);
> -       else
> +       else 
>                 cpustat->user = cputime64_add(cpustat->user, tmp);
>  
> +       cpustat->nicevalue[TASK_USER_PRIO(p)] = cputime64_add(cpustat->nicevalue[TASK_USER_PRIO(p)], tmp);
> +
>         cpuacct_update_stats(p, CPUACCT_STAT_USER, cputime);
>         /* Account for user time used */
>         acct_update_integrals(p); 

Yay! more senseless accounting.. we really need more of that. What's
even better is your data array being 320 bytes spanning 5 cachelines,
and thus the above almost guarantees a cacheline miss.

All round good stuff, and as DaveJ already pointed out, all without any
justification what so ever.