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

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Message-Id: <1179214707.32247.177.camel@localhost.localdomain>
Date:	Tue, 15 May 2007 17:38:27 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Tsutomu OWA <tsutomu.owa@...hiba.co.jp>
Cc:	Arnd Bergmann <arnd@...db.de>, linuxppc-dev@...abs.org,
	Thomas Gleixner <tglx@...utronix.de>, mingo@...e.hu,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 4/4] powerpc 2.6.21-rt1: reduce scheduling latency by
	changing tlb flush size


> +
> +#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.


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