[Xen-devel] RE: [RFC] [PATCH 0/2] Some clean-up to MCA handling

["Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>]

>-----Original Message-----
>From: Christoph Egger [mailto:Christoph.Egger@xxxxxxx]
>Sent: Monday, April 19, 2010 6:07 PM
>To: Jiang, Yunhong
>Cc: Frank.Vanderlinden@xxxxxxx; Keir Fraser; xen-devel@xxxxxxxxxxxxxxxxxxx
>Subject: Re: [RFC] [PATCH 0/2] Some clean-up to MCA handling
>
>On Monday 19 April 2010 10:58:44 Jiang, Yunhong wrote:
>> These two patches includes some clean-up/changes to MCA handling.
>>
>> The mce_extended.patch change the method to get the extended MCA
>> information. This change is somwhat straightforward and is easy to
>> understand. But please notice it changes some interface in
>> include/public/arch-x86/xen-mca.h.
>
>This breaks backward-compatibility. You can't change the API/ABI just for the
>sake of "easier" internal handling.
>
>Please explain:
>- what exactly is wrong with the interface as it is in upstream ?
>- what *requries* an API/ABI change ?

It is not "easier" internalhandling. In fact, it makes no difference to 
internal handling at all. The reason is:
1) In amd_f10.c, it will only occupy 4 mc_msr, while in Intel platform, it may 
occupy 32 mc_msr, that is sure to cost extra space. The mc_info buffer is quite 
limited and can't be expanded in run time, so reduce the size is quite 
important.
2) sizeof(void *) is different in 64 hypervisor and32 bit dom0. I'm not sure if 
it is tested in compatibility mode, which might be confused.

In fact, since we have mc_msrs included in mcinfo_extended already, the caller 
can get the size of the buffer quite easy.

Of course, if you *really* don't care the waste of size in AMD platform, it's 
ok for me. After all, in intel platform, either there is no extended 
information, or it will occupy all of them, so it really does not matter to me. 
But the (void*) issue should be resolved, I suspect.

How about your option to the other patch?

Thanks
--jyh

>
>Christoph
>
>
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