Re: [profile] fix timer interrupt livelock on 512x Altix

[Rusty Russell <rusty@rustcorp.com.au>]

On Tue, 2004-09-21 at 07:30, William Lee Irwin III wrote:
> +static void __profile_flip_buffers(void *unused)
> +{
> +	int cpu = smp_processor_id();
> +
> +	per_cpu(cpu_profile_flip, cpu) = !per_cpu(cpu_profile_flip, cpu);
> +}

Please: one point of per-cpu vars is that archs can choose to hold the
per-cpu offset in a reg, and derive smp_processor_id() from that.  By
doing the reverse, manually, you defeat this.  How about:

	int *flip = __get_cpu_var(cpu_profile_flip);
	*flip = !*flip;

> +
> +static void profile_flip_buffers(void)
> +{
> +	int i, j, cpu;
> +
> +	down(&profile_flip_mutex);
> +	j = per_cpu(cpu_profile_flip, get_cpu());
> +	put_cpu();

Similarly, this is equivalent to:
	j = __get_cpu_var(cpu_profile_flip);

Cheers,
Rusty.
-- 
Anyone who quotes me in their signature is an idiot -- Rusty Russell