A clocksource driver for HyperV

Ky Srinivasan ksrinivasan at novell.com
Wed Apr 7 18:20:29 UTC 2010



>>> On 4/5/2010 at  5:36 PM, in message <  4BBA57FB.2000406 at goop.org  >, Jeremy
Fitzhardinge <  jeremy at goop.org  > wrote: 
> On 04/05/2010 01:30 PM, Ky Srinivasan wrote:
>> +static cycle_t read_hv_clock(struct clocksource *arg)
>> +{
>> +	cycle_t current_tick;
>> +	/*
>> +	 * Read the partition counter to get the current tick count. This count
>> +	 * is set to 0 when the partition is created and is incremented in
>> +	 * 100 nanosecond units.
>> +	 */
>> +	rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick);
>> +	return current_tick;
>> +}
>> +
>> +static struct clocksource clocksource_hyperv = {
>> +	.name           = "hyperv_clocksource",
>>    
> 
> Seems like a redundantly long name; any use of this string is going to 
> be in a context where it is obviously a clocksource.  How about just 
> "hyperv"


> 
>> +	.rating         = 400, /* use this when running on Hyperv*/
>> +	.read           = read_hv_clock,
>> +	.mask           = CLOCKSOURCE_MASK(64),
>> +	.shift          = HV_CLOCK_SHIFT,
>> +};
>> +
>> +static struct dmi_system_id __initconst
>> +hv_timesource_dmi_table[] __maybe_unused  = {
>> +	{
>> +		.ident = "Hyper-V",
>> +		.matches = {
>> +			DMI_MATCH(DMI_SYS_VENDOR, "Microsoft Corporation"),
>> +			DMI_MATCH(DMI_PRODUCT_NAME, "Virtual Machine"),
>> +			DMI_MATCH(DMI_BOARD_NAME, "Virtual Machine"),
>> +		},
>> +	},
>> +	{ },
>> +};
>> +MODULE_DEVICE_TABLE(dmi, hv_timesource_dmi_table);
>>    
> 
> So you use the DMI signatures to determine whether the module is needed, 
> but cpuid to work out if the feature is present?
> 
>> +
>> +static struct pci_device_id __initconst
>> +hv_timesource_pci_table[] __maybe_unused = {
>> +	{ PCI_DEVICE(0x1414, 0x5353) }, /* VGA compatible controller */
>> +	{ 0 }
>> +};
>> +MODULE_DEVICE_TABLE(pci, hv_timesource_pci_table);
>>    
> 
> And/or PCI?
> 
> Seems a bit... ad-hoc?  Is this the official way to determine the 
> presence of Hyper-V?

The presence of HyperV and our ability to use the partition-wide counter obviously is checked via probing the cpuid leaves. The DMI/PCI signatures are used in auto-loading these modules.
> 
>> +
>> +
>> +static int __init hv_detect_hyperv(void)
>>    
> 
> This looks generally useful.  Should it be hidden away in the 
> clocksource driver, or in some common hyper-v code?  Do other hyper-v 
> drivers have versions of this?
Good point. Right now, I can think of  multiple drivers replicating this code. We could include hyperV detection code in cpu/hypervisor.c . I will spin up a patch for doing that shortly. 
> 
>> +{
>> +	u32 eax, ebx, ecx, edx;
>> +	static char hyp_signature[20];
>>    
> 20?  static?
> 
>> +
>> +	cpuid(1,&eax,&ebx,&ecx,&edx);
>> +	if (!(ecx&  HV_HYPERVISOR_PRESENT_BIT)) {
>> +		printk(KERN_WARNING
>> +			"Not on a Hypervisor\n");
>>    
> This just looks like noise, especially since it doesn't identify what is 
> generating the message.  And if you compile this code in as =y 
> (non-modular) then it will complain every boot.
> 
>> +		return 1;
>> +	}
>> +	cpuid(HV_CPUID_SIGNATURE,&eax,&ebx,&ecx,&edx);
>> +	*(u32 *)(hyp_signature + 0) = ebx;
>> +	*(u32 *)(hyp_signature + 4) = ecx;
>> +	*(u32 *)(hyp_signature + 8) = edx;
>> +	hyp_signature[12] = 0;
>> +
>> +	if ((eax<  HV_CPUID_MIN) || (strcmp("Microsoft Hv", hyp_signature))) {
>>    
> 
> memcmp, surely?
> 
>> +		printk(KERN_WARNING
>> +			"Not on HyperV; signature %s, eax %x\n",
>> +			hyp_signature, eax);
>> +		return 1;
>> +	}
>> +	/*
>> +	 * Extract the features, recommendations etc.
>> +	 */
>> +	cpuid(HV_CPUID_FEATURES,&eax,&ebx,&ecx,&edx);
>> +	if (!(eax&  0x10)) {
>> +		printk(KERN_WARNING "HyperV Time Ref Counter not available!\n");
>> +		return 1;
>> +	}
>> +
>> +	cpuid(HV_CPUID_RECOMMENDATIONS,&eax,&ebx,&ecx,&edx);
>> +	printk(KERN_INFO "HyperV recommendations: %x\n", eax);
>> +	printk(KERN_INFO "HyperV spin count: %x\n", ebx);
>> +	return 0;
>> +}
>> +
>> +
>> +static int __init init_hv_clocksource(void)
>> +{
>> +	if (hv_detect_hyperv())
>> +		return -ENODEV;


>> +	/*
>> +	 * The time ref counter in HyperV is in 100ns units.
>> +	 * The definition of mult is:
>> +	 * mult/2^shift = ns/cyc = 100
>> +	 * mult = (100<<  shift)
>> +	 */
>> +	clocksource_hyperv.mult = (100<<  HV_CLOCK_SHIFT);
>>    
> 
> Why not initialize this in the structure?  It's just 100<<22 isn't it?
> 
>> +	printk(KERN_INFO "Registering HyperV clock source\n");
>> +	return clocksource_register(&clocksource_hyperv);
>> +}
>> +
>> +module_init(init_hv_clocksource);
>> +MODULE_DESCRIPTION("HyperV based clocksource");
>> +MODULE_AUTHOR("K. Y. Srinivasan<  ksrinivasan at novell.com  >");
>> +MODULE_LICENSE("GPL");
>> Index: linux/drivers/staging/hv/Makefile
>> ===================================================================
>> --- linux.orig/drivers/staging/hv/Makefile	2010-04-05 13:02:06.000000000 -0600
>> +++ linux/drivers/staging/hv/Makefile	2010-04-05 13:02:13.000000000 -0600
>> @@ -1,4 +1,4 @@
>> -obj-$(CONFIG_HYPERV)		+= hv_vmbus.o
>> +obj-$(CONFIG_HYPERV)		+= hv_vmbus.o hv_timesource.o
>>   obj-$(CONFIG_HYPERV_STORAGE)	+= hv_storvsc.o
>>   obj-$(CONFIG_HYPERV_BLOCK)	+= hv_blkvsc.o
>>   obj-$(CONFIG_HYPERV_NET)	+= hv_netvsc.o
>>    

Jeremy, thank you for your comments. I am attaching the next version of this patch that addresses the comments I have gotten thus far.  

Regards,

K. Y 

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