Re: [Xen-devel] LVTPC masking in Intel VPMU code

["Shan, Haitao" <haitao.shan@xxxxxxxxx>]

Hi, Jan,

This is a pretty old code. :) I did not copy or borrow the oprofile and perf 
code at all. Thus, I am not aware of the quirk. (Actually, I don't know what 
quirk you mean).
For Xen's PMI handler, I just unmask the source and deliver a virtual one. Here 
in this code, I see I unmasked the physical one and mask the virtual LVTPC.

Can you tell me more about the oprofile/perf background?

Shan Haitao

-----Original Message-----
From: Jan Beulich [mailto:JBeulich@xxxxxxxx] 
Sent: Thursday, March 28, 2013 7:26 PM
To: Shan, Haitao
Cc: xen-devel; Boris Ostrovsky
Subject: Re: [Xen-devel] LVTPC masking in Intel VPMU code

>>> On 27.03.13 at 22:34, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx> wrote:
> Can someone explain why we have these lines in 
> vpmu_core2.c:core2_vpmu_do_interrupt():
>      apic_write_around(APIC_LVTPC, apic_read(APIC_LVTPC) & 
> ~APIC_LVT_MASKED);
>      ...
>      vlapic_set_reg(vlapic, APIC_LVTPC, vlapic_lvtpc | APIC_LVT_MASKED);
> 
> There is similar code in Linux oprofile with a comment that this is done 
> due to some sort of
> a quirk on P4 and PentiumM. Is this why it's in 
> core2_vpmu_do_interrupt() as well?
> 
> I don't see a quirk like this in Linux perf code.

Haitao, you contributed that code a long while back. Any comment?

Jan


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