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

  • To: Jan Beulich <JBeulich@xxxxxxxx>
  • From: "Shan, Haitao" <haitao.shan@xxxxxxxxx>
  • Date: Fri, 29 Mar 2013 09:12:07 +0000
  • Accept-language: en-US
  • Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, xen-devel <xen-devel@xxxxxxxxxxxxx>
  • Delivery-date: Fri, 29 Mar 2013 11:10:51 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xen.org>
  • Thread-index: AQHOK6b81ptL8Ujmj0mZ9O0owy9ceJi8Yizg
  • Thread-topic: [Xen-devel] LVTPC masking in Intel VPMU code

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) & 
>      ...
>      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?


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