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Drivers: hv: vmbus: Implement a clocksource based on the TSC page

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The current Hyper-V clock source is based on the per-partition reference counter
and this counter is being accessed via s synthetic MSR - HV_X64_MSR_TIME_REF_COUNT.
Hyper-V has a more efficient way of computing the per-partition reference
counter value that does not involve reading a synthetic MSR. We implement
a time source based on this mechanism.

Tested-by: Vivek Yadav <vyadav@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
K. Y. Srinivasan 2015-08-05 00:52:42 -07:00 committed by Greg Kroah-Hartman
parent bc609cb47f
commit ca9357bd26
3 changed files with 94 additions and 0 deletions
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2
arch/x86/include/uapi/asm/hyperv.h
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@ -27,6 +27,8 @@
#define HV_X64_MSR_VP_RUNTIME_AVAILABLE (1 << 0)
/* Partition Reference Counter (HV_X64_MSR_TIME_REF_COUNT) available*/
#define HV_X64_MSR_TIME_REF_COUNT_AVAILABLE (1 << 1)
/* Partition reference TSC MSR is available */
#define HV_X64_MSR_REFERENCE_TSC_AVAILABLE (1 << 9)
/* A partition's reference time stamp counter (TSC) page */
#define HV_X64_MSR_REFERENCE_TSC 0x40000021

83
drivers/hv/hv.c
View File

@ -133,6 +133,56 @@ static u64 do_hypercall(u64 control, void *input, void *output)
#endif /* !x86_64 */
}
#ifdef CONFIG_X86_64
static cycle_t read_hv_clock_tsc(struct clocksource *arg)
{
cycle_t current_tick;
struct ms_hyperv_tsc_page *tsc_pg = hv_context.tsc_page;
if (tsc_pg->tsc_sequence != -1) {
/*
* Use the tsc page to compute the value.
*/
while (1) {
cycle_t tmp;
u32 sequence = tsc_pg->tsc_sequence;
u64 cur_tsc;
u64 scale = tsc_pg->tsc_scale;
s64 offset = tsc_pg->tsc_offset;
rdtscll(cur_tsc);
/* current_tick = ((cur_tsc *scale) >> 64) + offset */
asm("mulq %3"
: "=d" (current_tick), "=a" (tmp)
: "a" (cur_tsc), "r" (scale));
current_tick += offset;
if (tsc_pg->tsc_sequence == sequence)
return current_tick;
if (tsc_pg->tsc_sequence != -1)
continue;
/*
* Fallback using MSR method.
*/
break;
}
}
rdmsrl(HV_X64_MSR_TIME_REF_COUNT, current_tick);
return current_tick;
}
static struct clocksource hyperv_cs_tsc = {
.name = "hyperv_clocksource_tsc_page",
.rating = 425,
.read = read_hv_clock_tsc,
.mask = CLOCKSOURCE_MASK(64),
.flags = CLOCK_SOURCE_IS_CONTINUOUS,
};
#endif
/*
* hv_init - Main initialization routine.
*
@ -142,7 +192,9 @@ int hv_init(void)
{
int max_leaf;
union hv_x64_msr_hypercall_contents hypercall_msr;
union hv_x64_msr_hypercall_contents tsc_msr;
void *virtaddr = NULL;
void *va_tsc = NULL;
memset(hv_context.synic_event_page, 0, sizeof(void *) * NR_CPUS);
memset(hv_context.synic_message_page, 0,
@ -186,6 +238,22 @@ int hv_init(void)
hv_context.hypercall_page = virtaddr;
#ifdef CONFIG_X86_64
if (ms_hyperv.features & HV_X64_MSR_REFERENCE_TSC_AVAILABLE) {
va_tsc = __vmalloc(PAGE_SIZE, GFP_KERNEL, PAGE_KERNEL);
if (!va_tsc)
goto cleanup;
hv_context.tsc_page = va_tsc;
rdmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr.as_uint64);
tsc_msr.enable = 1;
tsc_msr.guest_physical_address = vmalloc_to_pfn(va_tsc);
wrmsrl(HV_X64_MSR_REFERENCE_TSC, tsc_msr.as_uint64);
clocksource_register_hz(&hyperv_cs_tsc, NSEC_PER_SEC/100);
}
#endif
return 0;
cleanup:
@ -219,6 +287,21 @@ void hv_cleanup(void)
vfree(hv_context.hypercall_page);
hv_context.hypercall_page = NULL;
}
#ifdef CONFIG_X86_64
/*
* Cleanup the TSC page based CS.
*/
if (ms_hyperv.features & HV_X64_MSR_REFERENCE_TSC_AVAILABLE) {
clocksource_change_rating(&hyperv_cs_tsc, 10);
clocksource_unregister(&hyperv_cs_tsc);
hypercall_msr.as_uint64 = 0;
wrmsrl(HV_X64_MSR_REFERENCE_TSC, hypercall_msr.as_uint64);
vfree(hv_context.tsc_page);
hv_context.tsc_page = NULL;
}
#endif
}
/*

9
drivers/hv/hyperv_vmbus.h
View File

@ -517,6 +517,7 @@ struct hv_context {
u64 guestid;
void *hypercall_page;
void *tsc_page;
bool synic_initialized;
@ -560,6 +561,14 @@ struct hv_context {
extern struct hv_context hv_context;
struct ms_hyperv_tsc_page {
volatile u32 tsc_sequence;
u32 reserved1;
volatile u64 tsc_scale;
volatile s64 tsc_offset;
u64 reserved2[509];
};
struct hv_ring_buffer_debug_info {
u32 current_interrupt_mask;
u32 current_read_index;