linux-kernel - Re: [Xen-devel] Re: [patch 14/21] Xen-paravirt: Add XEN config options and disableunsupported config options.

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Date:	Fri, 16 Feb 2007 13:51:21 -0800
From:	Zachary Amsden <zach@...are.com>
To:	Keir Fraser <keir@...source.com>
CC:	Jeremy Fitzhardinge <jeremy@...p.org>,
	xen-devel@...ts.xensource.com, virtualization@...ts.osdl.org,
	Steven Hand <steven.hand@...cam.ac.uk>,
	linux-kernel@...r.kernel.org, Chris Wright <chrisw@...s-sol.org>,
	Andi Kleen <ak@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ian Pratt <Ian.Pratt@...source.com>,
	Christian Limpach <Christian.Limpach@...source.com>
Subject: Re: [Xen-devel] Re: [patch 14/21] Xen-paravirt: Add XEN config	options
 and disableunsupported config options.

Keir Fraser wrote:
> On 16/2/07 17:46, "Jeremy Fitzhardinge" <jeremy@...p.org> wrote:
>
>   
>> Keir Fraser wrote:
>>     
>>> This initial patchset does not include save/restore support anyway, so in
>>> fact it would be consistent to have CONFIG_PREEMPT configurable. I'm sure
>>> that we are going to have some nasty bugs to fix up as a result, but we
>>> can't fix them until we find them! Then we can convert our save/restore code
>>> to use the freezer before submitting it for inclusion.
>>>       
>> OK.  So that makes the only config restriction the 100Hz ticks.
>>     
>
> We can extend the Xen timer interface quite easily and get rid of this one
> too. In fact it doesn't *much* matter if the CONFIG_HZ differs from the Xen
> ticker rate -- we modified the Linux timer ISR to handle timer interrupts at
> arbitrary times already. The only drawback is that jiffies updates in burts
> if CONFIG_HZ is higher than the actual tick rate, and this can affect some
> calibration constants and cause Linux to print out some weird values at
> start-of-day.
>   

That's why we'd very much like to get a get_cpu_speed paravirt-op 
implemented.  I think this would be useful to work around these problems 
for Xen as well.

Zach
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