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Date: Thu, 31 May 2007 15:14:48 -0500
To: Jake Moilanen <moilanen@austin.ibm.com>
Subject: Re: [PATCH] Donate dedicated CPU cycles
Message-ID: <20070531201447.GA30760@lixom.net>
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From: olof@lixom.net (Olof Johansson)
Cc: linuxppc-dev@ozlabs.org, Paul Mackerras <paulus@samba.org>
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Hi,

On Thu, May 31, 2007 at 02:14:45PM -0500, Jake Moilanen wrote:
> A Power6 can give up CPU cycles on a dedicated CPU (as opposed to a
> shared CPU) to other shared processors if the administrator asks for it
> (via the HMC).
> 
> This patch enables that to work properly on P6.
> 
> This just involves setting a bit in the CAS structure as well as the
> VPA.  To donate cycles, a CPU has to have all SMT threads idle and w/
> donate bit set in the VPA.  Then call H_CEDE.

[...]

> Index: powerpc/arch/powerpc/platforms/pseries/setup.c
> ===================================================================
> --- powerpc.orig/arch/powerpc/platforms/pseries/setup.c
> +++ powerpc/arch/powerpc/platforms/pseries/setup.c
> @@ -399,6 +399,7 @@ static void pseries_dedicated_idle_sleep
>  	 * a good time to find other work to dispatch.
>  	 */
>  	get_lppaca()->idle = 1;
> +	get_lppaca()->cpuctls_task_attrs = 1;
>  
>  	/*
>  	 * We come in with interrupts disabled, and need_resched()
> @@ -431,6 +432,7 @@ static void pseries_dedicated_idle_sleep
>  
>  out:
>  	HMT_medium();
> +	get_lppaca()->cpuctls_task_attrs = 0;
>  	get_lppaca()->idle = 0;
>  }

Is this really the cpu controls task attribute field any more?  If this
is not just a flag (stored in a byte), the variable should be renamed
accordingly. If it is truly an attribute bitfield, then the attributes
should be named and constants used instead.


-Olof