Re: memtest 4.20+ does not work with -cpu host

[Peter Lieven <pl@dlhnet.de>]

On 13.09.2012 14:42, Gleb Natapov wrote:
> On Thu, Sep 13, 2012 at 02:05:23PM +0200, Peter Lieven wrote:
>> On 13.09.2012 10:05, Gleb Natapov wrote:
>>> On Thu, Sep 13, 2012 at 10:00:26AM +0200, Paolo Bonzini wrote:
>>>> Il 13/09/2012 09:57, Gleb Natapov ha scritto:
>>>>>>>>> #rdmsr -0 0x194
>>>>>>>>> 0000000000011100
>>>>>>>>> #rdmsr -0 0xce
>>>>>>>>> 00000c0004011103
>>>>>>> Yes, that can help implementing it in KVM.  But without a spec to
>>>>>>> understand what the bits actually mean, it's just as risky...
>>>>>>>
>>>>>>> Peter, do you have any idea where to get the spec of the memory
>>>>>>> controller MSRs in Nehalem and newer processors?  Apparently, memtest is
>>>>>>> using them (and in particular 0x194) to find the speed of the FSB, or
>>>>>>> something like that.
>>>>>>>
>>>>> Why would anyone will want to run memtest in a vm? May be just add those
>>>>> MSRs to ignore list and that's it.
>>>> >From the output it looks like it's basically a list of bits.  Returning
>>>> something sensible is better, same as for the speed scaling MSRs.
>>>>
>>> Everything is list of bits in computers :) At least 0xce is documented in  SDM.
>>> It cannot be implemented in a migration safe manner.
>> What do you suggest just say memtest does not work?
> Why do you want to run it in a guest?
Testing memory thorughput of different host memory layouts/settings 
(hugepages, ksm etc.).
Stress testing new settings and qemu-kvm builds.
Testing new nodes with a VM which claims all available pages. Its a lot 
easier than booting
a node with a CD and attaching to the Console.

This, of course, is all not missing critical and call also be done with 
cpu model qemu64. I just
came across memtest no longer working and where wondering if there is a 
general regressing.

BTW, from 
http://opensource.apple.com/source/xnu/xnu-1228.15.4/osfmk/i386/tsc.c?txt

#define MSR_FLEX_RATIO          0x194
#define MSR_PLATFORM_INFO       0x0ce
#define BASE_NHM_CLOCK_SOURCE   133333333ULL
#define CPUID_MODEL_NEHALEM     26

	switch (cpuid_info()->cpuid_model) {
	case CPUID_MODEL_NEHALEM: {
		uint64_t cpu_mhz;
		uint64_t msr_flex_ratio;
		uint64_t msr_platform_info;

		/* See if FLEX_RATIO is being used */
		msr_flex_ratio = rdmsr64(MSR_FLEX_RATIO);
		msr_platform_info = rdmsr64(MSR_PLATFORM_INFO);
		flex_ratio_min = (uint32_t)bitfield(msr_platform_info, 47, 40);
		flex_ratio_max = (uint32_t)bitfield(msr_platform_info, 15, 8);
		/* No BIOS-programed flex ratio. Use hardware max as default */
		tscGranularity = flex_ratio_max;
		if (msr_flex_ratio & bit(16)) {
		 	/* Flex Enabled: Use this MSR if less than max */
			flex_ratio = (uint32_t)bitfield(msr_flex_ratio, 15, 8);
			if (flex_ratio < flex_ratio_max)
				tscGranularity = flex_ratio;
		}

		/* If EFI isn't configured correctly, use a constant
		 * value. See 6036811.
		 */
		if (busFreq == 0)
			busFreq = BASE_NHM_CLOCK_SOURCE;

		cpu_mhz = tscGranularity * BASE_NHM_CLOCK_SOURCE;

	        kprintf("[NHM] Maximum Non-Turbo Ratio = [%d]\n",
			(uint32_t)tscGranularity);
	        kprintf("[NHM] CPU: Frequency          = %6d.%04dMhz\n",
			(uint32_t)(cpu_mhz / Mega), (uint32_t)(cpu_mhz % Mega));
		break;
             }



Peter