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authorBharat Bhushan <r65777@freescale.com>2012-04-18 10:01:19 +0400
committerAlexander Graf <agraf@suse.de>2012-05-06 18:19:07 +0400
commit6e35994d1f6831af1e5577e28c363c9137d7d597 (patch)
tree4c230223e9f76865a2bf01e4f4893b30fe2482b7 /arch/powerpc/kvm/emulate.c
parentcc902ad4f2b7cd3dd2cc268c63f6fb99fb1abf0f (diff)
downloadlinux-6e35994d1f6831af1e5577e28c363c9137d7d597.tar.xz
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 <bharat.bhushan@freescale.com> Signed-off-by: Alexander Graf <agraf@suse.de>
Diffstat (limited to 'arch/powerpc/kvm/emulate.c')
-rw-r--r--arch/powerpc/kvm/emulate.c9
1 files changed, 7 insertions, 2 deletions
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 <linux/types.h>
#include <linux/string.h>
#include <linux/kvm_host.h>
+#include <linux/clockchips.h>
#include <asm/reg.h>
#include <asm/time.h>
@@ -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);