Re: [PATCH -tip 1/3] x86, mce: Add mce_threshold option for intel cmci

Andi Kleen
2009-03-31T08:08:07Z

Hidetoshi Seto wrote:
> Andi Kleen wrote:
>> To turn it off you would need to disable the CMCI enable bit
>> completely.
>
> mce_threshold=0 discourages CMCI initialization.
> The CMCI enable bits are kept in off states in this case.

True, I missed that earlier. Still a different option would be better.

>
>> However I expect that this will be not a good idea to ever use on Nehalem
>> class systems at least because without CMCI the machine check code cannot
>> handle shared banks correctly and you'll get duplicated events from them.
>> And on non Nehalem systems there is no CMCI anyways, so it'll be always
>> off.
>
> One question is that even if one clears record in a shared bank, others
> sharing the bank still can retrieve same record? Or the duplication of
> recored only happens if a shared bank is polled by multiple cpu in parallel
> at same time?

Only when multiple CPUs poll (or machine check) at the same time.

>
> So old kernel without CMCI support running on new Nehalem class system will
> make duplicated records, right?

Occasionally when it races yes.

> Doesn't it impact to current distro like RHEL5?

Yes, somewhat. The bigger problem there is actually lack of broadcast handling,
that often leads to incorrect reporting of fatal MCEs.

-Andi