On 26.01.2010, at 10:41, Sheng Yang wrote: > The default action of coalesced MMIO is, cache the writing in buffer, until: > 1. The buffer is full. > 2. Or the exit to QEmu due to other reasons. > > But this would result in a very late writing in some condition. > 1. The each time write to MMIO content is small. > 2. The writing interval is big. > 3. No need for input or accessing other devices frequently. > > This issue was observed in a experimental embbed system. The test image > simply print "test" every 1 seconds. The output in QEmu meets expectation, > but the output in KVM is delayed for seconds. > > Per Avi's suggestion, I hooked flushing coalesced MMIO buffer in VGA update > handler. By this way, We don't need vcpu explicit exit to QEmu to > handle this issue. > > Signed-off-by: Sheng Yang <sheng@xxxxxxxxxxxxxxx> > --- > cpu-all.h | 2 ++ > exec.c | 6 ++++++ > kvm-all.c | 21 +++++++++++++-------- > kvm.h | 1 + > vl.c | 2 ++ > 5 files changed, 24 insertions(+), 8 deletions(-) > > diff --git a/cpu-all.h b/cpu-all.h > index 57b69f8..1ccc9a8 100644 > --- a/cpu-all.h > +++ b/cpu-all.h > @@ -915,6 +915,8 @@ void qemu_register_coalesced_mmio(target_phys_addr_t addr, ram_addr_t size); > > void qemu_unregister_coalesced_mmio(target_phys_addr_t addr, ram_addr_t size); > > +void qemu_flush_coalesced_mmio_buffer(void); > + > /*******************************************/ > /* host CPU ticks (if available) */ > > diff --git a/exec.c b/exec.c > index 1190591..6875370 100644 > --- a/exec.c > +++ b/exec.c > @@ -2406,6 +2406,12 @@ void qemu_unregister_coalesced_mmio(target_phys_addr_t addr, ram_addr_t size) > kvm_uncoalesce_mmio_region(addr, size); > } > > +void qemu_flush_coalesced_mmio_buffer(void) > +{ > + if (kvm_enabled()) > + kvm_flush_coalesced_mmio_buffer(); > +} > + > ram_addr_t qemu_ram_alloc(ram_addr_t size) > { > RAMBlock *new_block; > diff --git a/kvm-all.c b/kvm-all.c > index 15ec38e..889fc42 100644 > --- a/kvm-all.c > +++ b/kvm-all.c > @@ -59,6 +59,7 @@ struct KVMState > int vmfd; > int regs_modified; > int coalesced_mmio; > + struct kvm_coalesced_mmio_ring *coalesced_mmio_ring; I guess this needs to be guarded by an #ifdef? Alex-- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html