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: <200705141640.02561.arnd@arndb.de>
Date:	Mon, 14 May 2007 16:40:02 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linuxppc-dev@...abs.org
Cc:	Tsutomu OWA <tsutomu.owa@...hiba.co.jp>,
	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

On Monday 14 May 2007, Tsutomu OWA wrote:
> --- linux-2.6.21-rt1/include/asm-powerpc/tlbflush.h     2007-04-26 12:08:32.000000000 +0900
> +++ rt/include/asm-powerpc/tlbflush.h   2007-05-14 16:12:47.000000000 +0900
> @@ -25,7 +25,12 @@ struct mm_struct;
>  #include <linux/percpu.h>
>  #include <asm/page.h>
>  
> +#if defined(CONFIG_PPC_CELLEB) && defined(CONFIG_PREEMPT_RT)
> +/* Since tlb flush takes long time on Celleb, reduce it to 1 when Celleb && RT */
> +#define PPC64_TLB_BATCH_NR 1
> +#else
>  #define PPC64_TLB_BATCH_NR 192
> +#endif /* defined(CONFIG_PPC_CELLEB) && defined(CONFIG_PREEMPT_RT) */

With this code, you get silent side-effects of enabling PPC_CELLEB
along with another platform.

Maybe instead you should change the hpte_need_flush() to always flush
when running on the celleb platform and PREEMPT_RT is enabled.

	Arnd <><
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