69 lines
2.6 KiB
Diff
69 lines
2.6 KiB
Diff
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# HG changeset patch
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# User Keir Fraser <keir.fraser@citrix.com>
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# Date 1284739161 -3600
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# Node ID 632c02167f97bb2bd25571b2780425b9b75949b4
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# Parent 1b05090854ba83576aa8399fa70e481f5b602417
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hvm pmtimer: correct pmtimer accuracy
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Several seconds of backward time drift per minute can be seen on a
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RHEL6 HVM guest by switching the clocksource to 'acpi_pm' and then
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running gettimeofday() in a loop. This is due to the accumulation
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of small inaccuracies that are caused by shifting out the lower 32
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bits when pmt_update_time() computes 'tmr_val'.
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The patch makes sure that the lower 32 bits of the computed value
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are not lost. They are saved in a new field 'not_accounted' in the
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PMTState structure and are accounted the next time pmt_update_time()
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is called.
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From: Ulrich Obergfell <uobergfe@redhat.com>
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Signed-off-by: Keir Fraser <keir.fraser@citrix.com>
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--- a/xen/arch/x86/hvm/pmtimer.c
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+++ b/xen/arch/x86/hvm/pmtimer.c
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@@ -83,14 +83,16 @@ void hvm_acpi_sleep_button(struct domain
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* since the last time we did that. */
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static void pmt_update_time(PMTState *s)
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{
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- uint64_t curr_gtime;
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+ uint64_t curr_gtime, tmp;
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uint32_t msb = s->pm.tmr_val & TMR_VAL_MSB;
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ASSERT(spin_is_locked(&s->lock));
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/* Update the timer */
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curr_gtime = hvm_get_guest_time(s->vcpu);
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- s->pm.tmr_val += ((curr_gtime - s->last_gtime) * s->scale) >> 32;
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+ tmp = ((curr_gtime - s->last_gtime) * s->scale) + s->not_accounted;
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+ s->not_accounted = (uint32_t)tmp;
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+ s->pm.tmr_val += tmp >> 32;
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s->pm.tmr_val &= TMR_VAL_MASK;
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s->last_gtime = curr_gtime;
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@@ -257,6 +259,7 @@ static int pmtimer_load(struct domain *d
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/* Calculate future counter values from now. */
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s->last_gtime = hvm_get_guest_time(s->vcpu);
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+ s->not_accounted = 0;
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/* Set the SCI state from the registers */
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pmt_update_sci(s);
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@@ -276,6 +279,7 @@ void pmtimer_init(struct vcpu *v)
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spin_lock_init(&s->lock);
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s->scale = ((uint64_t)FREQUENCE_PMTIMER << 32) / SYSTEM_TIME_HZ;
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+ s->not_accounted = 0;
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s->vcpu = v;
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/* Intercept port I/O (need two handlers because PM1a_CNT is between
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--- a/xen/include/asm-x86/hvm/vpt.h
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+++ b/xen/include/asm-x86/hvm/vpt.h
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@@ -117,6 +117,7 @@ typedef struct PMTState {
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struct hvm_hw_pmtimer pm; /* 32bit timer value */
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struct vcpu *vcpu; /* Keeps sync with this vcpu's guest-time */
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uint64_t last_gtime; /* Last (guest) time we updated the timer */
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+ uint32_t not_accounted; /* time not accounted at last update */
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uint64_t scale; /* Multiplier to get from tsc to timer ticks */
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struct timer timer; /* To make sure we send SCIs */
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spinlock_t lock;
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