Re: [Xen-devel] xen cpuidle c states

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

I suggest add a few more printks to find out what's going on. E.g., what is
the value of xen_cpuidle near the end of arch/x86/setup.c:__start_xen().

How do you know only C1 is being used: is that what xenpm tells you? There
could be other reasons deeper sleeps are unavailable, such as dom0 not
informing Xen about their availability (misconfigured dom0 kernel?).

 -- Keir

On 05/11/2009 09:30, "Andrew Lyon" <andrew.lyon@xxxxxxxxx> wrote:

> Hi,
> 
> I've been looking into cpuidle c state usage on my Xeon based xen
> servers and I've noticed a couple of things I don't understand:
> 
> The xenpm documentation at http://wiki.xensource.com/xenwiki/xenpm it
> states that  "In xen3.4, cpuidle is enabled by default since c/s
> 19421.", but just over a month later that change was reversed by c/s
> 19545 with  comment "x86: Disable cpuidle by default unless hpet
> broadcast is available."
> 
> So I started looking at the code to see if there would be any messages
> indicating whether hpet broadcast/cpuidle was enabled or not, and in
> xen/arch/x86/time.c I found the following code which I am struggling
> to make sense of:
> 
>   /*
>      * If we do not rely on PIT CH0 then we can use HPET for one-shot timer
>      * emulation when entering deep C states.
>      * XXX dom0 may rely on RTC interrupt delivery, so only enable
>      * hpet_broadcast if FSB mode available or if force_hpet_broadcast.
>      */
>     if ( xen_cpuidle && !boot_cpu_has(X86_FEATURE_ARAT) )
>     {
>         hpet_broadcast_init();
>         if ( !hpet_broadcast_is_available() )
>         {
>             if ( xen_cpuidle == -1 )
>             {
>                 xen_cpuidle = 0;
>                 printk("CPUIDLE: disabled due to no HPET. "
>                        "Force enable with 'cpuidle'.\n");
>             }
>             else
>             {
>                 printk("HPET broadcast init failed, turn to PIT
> broadcast.\n");
>                 return 0;
>             }
>         }
>     }
> 
> 
> Neither of the messages above appear in the dmesg on my Xeon based xen
> servers, and they only enter C1 state, I've tried adding cpuidle to
> the xen kernel parameters but it makes no difference.
> 
> I'm probably just not understanding the code properly but it doesn't
> look like it would behave as the documentation or commit comments
> suggest it should....
> 
> Andy
> 
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