Re: [patch 4/4] powerpc 2.6.21-rt1: reduce scheduling latency by changing tlb flush size

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

> +
> +#ifdef CONFIG_PREEMPT_RT
> +	/*
> +	 * Since flushing tlb needs expensive hypervisor call(s) on celleb,
> +	 * always flush it on RT to reduce scheduling latency.
> +	 */
> +	if (machine_is(celleb)) {
> +		flush_tlb_pending();
> +		return;
> +	}
> +#endif /* CONFIG_PREEMPT_RT */
> +
>  	if (i >= PPC64_TLB_BATCH_NR)
>  		flush_tlb_pending();
>  }

Any reason to do that only on celleb ? :-)

Also, we might want to still batch, though in smaller amount. Have you measured
the time it takes ? We might want to modulate the amount based on wether we
are using native hash tables or an hypervisor.

Ben.