linux-kernel - Re: [patch] Mixed Madison and Montecito system support

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Date:	Mon, 23 Oct 2006 13:56:43 -0700
From:	"Luck, Tony" <tony.luck@...el.com>
To:	Russ Anderson <rja@....com>
Cc:	linux-ia64@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [patch] Mixed Madison and Montecito system support

Cc: linux-kernel for generic bit of this change.  Rest of patch was
posted to linux-ia64: http://marc.theaimsgroup.com/?l=linux-ia64&m=116070997529216&w=2

On Thu, Oct 12, 2006 at 10:25:58PM -0500, Russ Anderson wrote:
>  int sched_create_sysfs_power_savings_entries(struct sysdev_class *cls)
>  {
> -	int err = 0;
> +	int err = 0, c;
>  
>  #ifdef CONFIG_SCHED_SMT
> -	if (smt_capable())
> -		err = sysfs_create_file(&cls->kset.kobj,
> +	for_each_online_cpu(c)
> +		if (smt_capable(c)) {
> +			err = sysfs_create_file(&cls->kset.kobj,
>  					&attr_sched_smt_power_savings.attr);
> +			break;
> +		}
>  #endif

What if you booted an all-Madison system, and then hot-plugged some
Montecitos later?  Either we'd need the hotplug cpu code to run through
this routine again to re-test whether any cpu has multi-thread support
(it doesn't look like it does that now).

Or perhaps it would be simpler to dispense with this test and always
call sysfs_create_file() here (still inside CONFIG_SCHED_SMT) so that
the hook is always present to tune the scheduler (even if it may be
ineffective on a no-smt system)?

-Tony
-
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