linux-kernel - Re: [PATCH v2 1/3] hrtimer: add hrtimer_init

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Date:	Wed, 12 Sep 2012 16:26:24 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, ak@...ux.intel.com,
	zheng.z.yan@...el.com, robert.richter@....com,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2 1/3] hrtimer: add hrtimer_init_cpu()

I'm rather sure Thomas would want to know about this..


On Wed, 2012-09-12 at 16:13 +0200, Stephane Eranian wrote:
> hrtimer_init() assumes it is called for the current CPU
> as it accesses per-cpu variables (hrtimer_bases).
> 
> However, there can be cases where a hrtimer is initialized
> from a different CPU, so add an entry point to make this
> more explicit.
> 
> Signed-off-by: Stephane Eranian <eranian@...gle.com>
> ---
>  include/linux/hrtimer.h |    3 +++
>  kernel/hrtimer.c        |   17 ++++++++++++-----
>  2 files changed, 15 insertions(+), 5 deletions(-)
> 

> +static void __hrtimer_init(int cpu, struct hrtimer *timer, clockid_t clock_id,
>  			   enum hrtimer_mode mode)
>  {
>  	struct hrtimer_cpu_base *cpu_base;
> @@ -1154,7 +1154,7 @@ static void __hrtimer_init(struct hrtimer *timer, clockid_t clock_id,
>  
>  	memset(timer, 0, sizeof(struct hrtimer));
>  
> -	cpu_base = &__raw_get_cpu_var(hrtimer_bases);
> +	cpu_base = &per_cpu(hrtimer_bases, cpu);
>  
>  	if (clock_id == CLOCK_REALTIME && mode != HRTIMER_MODE_ABS)
>  		clock_id = CLOCK_MONOTONIC;


I don't see the point, one of the first things
__hrtimer_start_range_ns() does is switch_hrtimer_base() to swizzle it
to the calling CPUs base.

And since all the perf event rotation muck is strictly per cpu that all
should work out just fine, no?
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