On Mon, Jan 25, 2010 at 03:46:44PM +0800, 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.
Sheng,
Can you send this to QEMU upstream first, since the feature is present
there.
> Signed-off-by: Sheng Yang <sheng@xxxxxxxxxxxxxxx>
> ---
> cpu-all.h | 2 ++
> exec.c | 6 ++++++
> kvm-all.c | 20 ++++++++++++++++++++
> qemu-kvm.c | 9 +++++++--
> qemu-kvm.h | 2 ++
> vl.c | 2 ++
> 6 files changed, 39 insertions(+), 2 deletions(-)
>
> diff --git a/cpu-all.h b/cpu-all.h
> index 8ed76c7..51effc0 100644
> --- a/cpu-all.h
> +++ b/cpu-all.h
> @@ -916,6 +916,8 @@ 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 99e88e1..40c01a1 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -2424,6 +2424,12 @@ 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();
> +}
> +
> #ifdef __linux__
>
> #include <sys/vfs.h>
> diff --git a/kvm-all.c b/kvm-all.c
> index 0423fff..3d9fcc0 100644
> --- a/kvm-all.c
> +++ b/kvm-all.c
> @@ -25,6 +25,9 @@
> #include "hw/hw.h"
> #include "gdbstub.h"
> #include "kvm.h"
> +#ifndef KVM_UPSTREAM
> +#include "libkvm.h"
> +#endif
>
> #ifdef KVM_UPSTREAM
> /* KVM uses PAGE_SIZE in it's definition of COALESCED_MMIO_MAX */
> @@ -385,6 +388,23 @@ int kvm_uncoalesce_mmio_region(target_phys_addr_t start, ram_addr_t size)
> return ret;
> }
>
> +void kvm_flush_coalesced_mmio_buffer(void)
> +{
> +#ifdef KVM_CAP_COALESCED_MMIO
> + if (kvm_state->coalesced_mmio_ring) {
> + struct kvm_coalesced_mmio_ring *ring =
> + kvm_state->coalesced_mmio_ring;
> + while (ring->first != ring->last) {
> + cpu_physical_memory_rw(ring->coalesced_mmio[ring->first].phys_addr,
> + &ring->coalesced_mmio[ring->first].data[0],
> + ring->coalesced_mmio[ring->first].len, 1);
> + smp_wmb();
Tab breakage.
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