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 | 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();
+ ring->first = (ring->first + 1) % KVM_COALESCED_MMIO_MAX;
+ }
+ }
+#endif
+}
+
int kvm_check_extension(KVMState *s, unsigned int extension)
{
int ret;
diff --git a/qemu-kvm.c b/qemu-kvm.c
index 599c3d6..70d7658 100644
--- a/qemu-kvm.c
+++ b/qemu-kvm.c
@@ -463,6 +463,12 @@ static void kvm_create_vcpu(CPUState *env, int id)
goto err_fd;
}
+#ifdef KVM_CAP_COALESCED_MMIO
+ if (kvm_state->coalesced_mmio && !kvm_state->coalesced_mmio_ring)
+ kvm_state->coalesced_mmio_ring = (void *) env->kvm_run +
+ kvm_state->coalesced_mmio * PAGE_SIZE;
+#endif
+
return;
err_fd:
close(env->kvm_fd);
@@ -927,8 +933,7 @@ int kvm_run(CPUState *env)
#if defined(KVM_CAP_COALESCED_MMIO)
if (kvm_state->coalesced_mmio) {
- struct kvm_coalesced_mmio_ring *ring =
- (void *) run + kvm_state->coalesced_mmio * PAGE_SIZE;
+ 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],
diff --git a/qemu-kvm.h b/qemu-kvm.h
index 6b3e5a1..066e1c0 100644
--- a/qemu-kvm.h
+++ b/qemu-kvm.h
@@ -435,6 +435,7 @@ int kvm_register_coalesced_mmio(kvm_context_t kvm, uint64_t addr,
uint32_t size);
int kvm_unregister_coalesced_mmio(kvm_context_t kvm, uint64_t addr,
uint32_t size);
+void kvm_flush_coalesced_mmio_buffer(void);
/*!
* \brief Create a memory alias
@@ -1144,6 +1145,7 @@ typedef struct KVMState {
int fd;
int vmfd;
int coalesced_mmio;
+ struct kvm_coalesced_mmio_ring *coalesced_mmio_ring;
int broken_set_mem_region;
int migration_log;
int vcpu_events;
diff --git a/vl.c b/vl.c
index 9edea10..f39ad56 100644
--- a/vl.c
+++ b/vl.c
@@ -3227,6 +3227,7 @@ static void gui_update(void *opaque)
DisplayState *ds = opaque;
DisplayChangeListener *dcl = ds->listeners;
+ qemu_flush_coalesced_mmio_buffer();
dpy_refresh(ds);
while (dcl != NULL) {
@@ -3242,6 +3243,7 @@ static void nographic_update(void *opaque)
{
uint64_t interval = GUI_REFRESH_INTERVAL;
+ qemu_flush_coalesced_mmio_buffer();
qemu_mod_timer(nographic_timer, interval + qemu_get_clock(rt_clock));
}
--
1.5.4.5
--
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