Date: Thu, 10 Mar 2016 09:42:51 -0500
From: Paul Gortmaker <paul.gortmaker@windriver.com>
To: Toshi Kani <toshi.kani@hpe.com>
CC: Borislav Petkov <bp@suse.de>,
        Richard Purdie <richard.purdie@linuxfoundation.org>,
        Toshi Kani <toshi.kani@hp.com>,
        Bruce Ashfield <bruce.ashfield@windriver.com>,
        "Hart, Darren" <darren.hart@intel.com>,
        "saul.wold" <saul.wold@intel.com>, <linux-kernel@vger.kernel.org>
Subject: Re: runtime regression with "x86/mm/pat: Emulate PAT when it is
 disabled"
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[Re: runtime regression with "x86/mm/pat: Emulate PAT when it is disabled"] On 07/03/2016 (Mon 18:35) Toshi Kani wrote:

> On Mon, 2016-03-07 at 17:56 -0700, Toshi Kani wrote:

[...]

> And also an output of /proc/cpuinfo, please?

Here is the output of /proc/cpuinfo in the guest session, while
running on pentium dual core as host (no vmx):


processor	: 0
vendor_id	: GenuineIntel
cpu family	: 6
model		: 6
model name	: QEMU Virtual CPU version 2.5+
stepping	: 3
cpu MHz		: 2593.449
cache size	: 4096 KB
physical id	: 0
siblings	: 1
core id		: 0
cpu cores	: 1
apicid		: 0
initial apicid	: 0
fdiv_bug	: no
f00f_bug	: no
coma_bug	: no
fpu		: yes
fpu_exception	: yes
cpuid level	: 4
wp		: yes
flags		: fpu de pse tsc msr pae mce cx8 apic sep pge cmov mmx fxsr sse sse2 pni hypervisor
bugs		:
bogomips	: 5186.89
clflush size	: 32
cache_alignment	: 32
address sizes	: 36 bits physical, 32 bits virtual
power management:

Paul.
--

> 
> I think I know what's going on. ?I noticed that you have the following
> message in your dmesg files.
> 
> ?[????0.000000] MTRR: Disabled
> 
> MTRR is set to disabled when your CPU is Intel but does not support MTRR.
> ?Perhaps, QEMU does not emulate MTRR?
> 
> pat_init() is not called when MTRR is disabled. ?I think this dependency is
> wrong, and it needs to be fixed.
> 
> This issue has been there for a long time, and you have been running
> essentially as PAT disabled in the past. ?The commit in question simply
> detected this issue.
> 
> Thanks,
> -Toshi