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From: Nishanth Aravamudan <nacc@us.ibm.com>
To: Anton Blanchard <anton@samba.org>
Cc: paulus@samba.org, linuxppc-dev@lists.ozlabs.org, miltonm@bga.com
Subject: Re: [PATCH] rtas: Only sleep in rtas_busy_delay if we have useful work to do
Date: Thu, 7 Apr 2011 11:11:49 -0700	[thread overview]
Message-ID: <20110407181149.GA3851@us.ibm.com> (raw)
In-Reply-To: <20110407215407.4f6ca50f@kryten>

On 07.04.2011 [21:54:07 +1000], Anton Blanchard wrote:
> 
> RTAS returns extended error codes as a hint of how long the
> OS might want to wait before retrying a call. If we have nothing
> else useful to do we may as well call back straight away.
> 
> This was found when testing the new dynamic dma window feature.
> Firmware split the zeroing of the TCE table into 32k chunks but
> returned 9901 (which is a suggested wait of 10ms). All up this took
> about 10 minutes to complete since msleep is jiffies based and will
> round 10ms up to 20ms.
> 
> With the patch below we take 3 seconds to complete the same test.
> The hint firmware is returning in the RTAS call should definitely
> be decreased, but even if we slept 1ms each iteration this would
> take 32s.
> 
> Signed-off-by: Anton Blanchard <anton@samba.org>

Acked-by: Nishanth Aravamudan <nacc@us.ibm.com>

> ---
> 
> Index: linux-2.6/arch/powerpc/kernel/rtas.c
> ===================================================================
> --- linux-2.6.orig/arch/powerpc/kernel/rtas.c	2011-04-05 11:19:35.023234011 +1000
> +++ linux-2.6/arch/powerpc/kernel/rtas.c	2011-04-07 21:25:24.646414629 +1000
> @@ -494,7 +494,7 @@ unsigned int rtas_busy_delay(int status)
> 
>  	might_sleep();
>  	ms = rtas_busy_delay_time(status);
> -	if (ms)
> +	if (ms && need_resched())
>  		msleep(ms);
> 
>  	return ms;

      reply	other threads:[~2011-04-07 18:12 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-04-07 11:54 [PATCH] rtas: Only sleep in rtas_busy_delay if we have useful work to do Anton Blanchard
2011-04-07 18:11 ` Nishanth Aravamudan [this message]

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