Re: perf hw in kexeced kernel broken in tip

Yinghai Lu
2010-12-08T19:22:43Z

On 12/08/2010 11:17 AM, Peter Zijlstra wrote:
> On Wed, 2010-12-08 at 11:05 -0800, Yinghai Lu wrote:
>> On 12/08/2010 11:01 AM, Don Zickus wrote:
>>> On Wed, Dec 08, 2010 at 10:43:14AM -0800, Yinghai Lu wrote:
>>>>
>>>> can you add sth force_... in command line to take over ownership of perf from BIOS or previous kernel ?
>>>>
>>>> then still can use perf etc after we kexec from RHEL or SLES kernel to later kernel ( from 2.6.37)
>>>
>>> My understand is that you can't because the BIOS is actively using it
>>> behind the scenes of the kernel (well during an SMI). I have a machine
>>> where I tried to force take it but it still stopped triggering interrupts.
>>
>> how about second case: kexec from RHEL 6 stock kernel to upstream kernel ?
>
> Its impossible to distinguish between a BIOS having claimed a counter
> and a previous kernel not having shut things down properly.
>
> The best we can do is allow a force parameter and let the user keep all
> pieces when he uses it.

ok, thanks.