On Fri, Oct 14, 2011 at 07:30:09AM +0200, Alexander Graf wrote: > > On 14.10.2011, at 07:19, David Gibson wrote: > > > 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 <an...@au1.ibm.com> > > Signed-off-by: David Gibson <da...@gibson.dropbear.id.au> > > --- > > hw/ppc.c | 25 ++++++++++++++----------- > > 1 files changed, 14 insertions(+), 11 deletions(-) > > > > diff --git a/hw/ppc.c b/hw/ppc.c > > index 25b59dd..87aa4e5 100644 > > --- a/hw/ppc.c > > +++ b/hw/ppc.c > > @@ -658,21 +658,24 @@ static void __cpu_ppc_store_decr (CPUState *env, > > uint64_t *nextp, > > Do we ever call store_decr in the kvm case? Isn't that only called > from emulated mtdec?
Yes, from cpu_ppc_set_tb_clk(). Anton observed the kvm exits in the wild, they're not theoretical. Agh, which reminds me, I forgot to fixup the git author again. The patch should show authorship by Anton Blanchard <an...@au1.ibm.com>, as in the s-o-b. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson