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ppc: Avoid decrementer related kvm exits

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In __cpu_ppc_store_decr(), we set up a regular timer used to trigger
decrementer interrupts.  This is necessary to implement the decrementer
properly under TCG, but is unnecessary under KVM (true for both Book3S-PR
and Book3S-HV KVM variants), because the kernel handles generating and
delivering decrementer exceptions.

Under kvm, in fact, the timer causes expensive and unnecessary exits from
kvm to qemu.  This patch, therefore, disables setting the timer when kvm
is in use.

Signed-off-by: Anton Blanchard <anton@au1.ibm.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>
This commit is contained in:
David Gibson 2011-10-16 19:26:17 +00:00 committed by Alexander Graf
parent f0ad8c3401
commit 55f7d4b09e
1 changed files with 6 additions and 0 deletions
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6
hw/ppc.c
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@ -662,6 +662,12 @@ static void __cpu_ppc_store_decr (CPUState *env, uint64_t *nextp,
LOG_TB("%s: %08" PRIx32 " => %08" PRIx32 "\n", __func__,
decr, value);
if (kvm_enabled()) {
/* KVM handles decrementer exceptions, we don't need our own timer */
return;
}
now = qemu_get_clock_ns(vm_clock);
next = now + muldiv64(value, get_ticks_per_sec(), tb_env->decr_freq);
if (is_excp) {