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 sh...@linux.intel.com
---
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--
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