From 6e35994d1f6831af1e5577e28c363c9137d7d597 Mon Sep 17 00:00:00 2001 From: Bharat Bhushan Date: Wed, 18 Apr 2012 06:01:19 +0000 Subject: KVM: PPC: Use clockevent multiplier and shifter for decrementer Time for which the hrtimer is started for decrementer emulation is calculated using tb_ticks_per_usec. While hrtimer uses the clockevent for DEC reprogramming (if needed) and which calculate timebase ticks using the multiplier and shifter mechanism implemented within clockevent layer. It was observed that this conversion (timebase->time->timebase) are not correct because the mechanism are not consistent. In our setup it adds 2% jitter. With this patch clockevent multiplier and shifter mechanism are used when starting hrtimer for decrementer emulation. Now the jitter is < 0.5%. Signed-off-by: Bharat Bhushan Signed-off-by: Alexander Graf --- arch/powerpc/kvm/emulate.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) (limited to 'arch/powerpc/kvm') diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c index afc9154f1aef..b5872f61a213 100644 --- a/arch/powerpc/kvm/emulate.c +++ b/arch/powerpc/kvm/emulate.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #include @@ -104,8 +105,12 @@ void kvmppc_emulate_dec(struct kvm_vcpu *vcpu) */ dec_time = vcpu->arch.dec; - dec_time *= 1000; - do_div(dec_time, tb_ticks_per_usec); + /* + * Guest timebase ticks at the same frequency as host decrementer. + * So use the host decrementer calculations for decrementer emulation. + */ + dec_time = dec_time << decrementer_clockevent.shift; + do_div(dec_time, decrementer_clockevent.mult); dec_nsec = do_div(dec_time, NSEC_PER_SEC); hrtimer_start(&vcpu->arch.dec_timer, ktime_set(dec_time, dec_nsec), HRTIMER_MODE_REL); -- cgit v1.2.3