On 2023/9/4 21:27, Yong Huang wrote:
On Fri, Sep 1, 2023 at 10:19 AM <alloc.yo...@outlook.com
<mailto:alloc.yo...@outlook.com>> wrote:
From: alloc <alloc.yo...@outlook.com <mailto:alloc.yo...@outlook.com>>
Timeout functions like usleep can return early on signal, which reduces
more dirty pages than expected. In dirtylimit case, dirtyrate meter
thread needs to kick all vcpus out to sync. The callchain:
vcpu_calculate_dirtyrate
global_dirty_log_sync
memory_global_dirty_log_sync
kvm_log_sync_global
kvm_dirty_ring_flush
kvm_cpu_synchronize_kick_all <---- send vcpu signal
For long time sleep, use qemu_cond_timedwait_iothread to handle cpu stop
event.
The Dirty Limit algorithm seeks to keep the vCPU dirty page rate within
the set limit; since it focuses more emphasis on processing time and
precision, I feel that improvement should strive for the same result.
Could you please provide the final test results showing the impact of
that improvement?
The kvm_cpu_sync in dirty ring flush has to wait all vcpu to exit to run
sync action, while the vcpu sleep may blocks this. Before this patch,
the kick can reduce early vcpu return and add more dirty pages. It seems
the kvm_cpu_sync conflicts with vcpu sleep, why not measure dirty rate
when dirty ring fulls?
Signed-off-by: alloc <alloc.yo...@outlook.com
<mailto:alloc.yo...@outlook.com>>
---
softmmu/dirtylimit.c | 19 +++++++++++++++++--
1 file changed, 17 insertions(+), 2 deletions(-)
diff --git a/softmmu/dirtylimit.c b/softmmu/dirtylimit.c
index fa959d7743..ee938c636d 100644
--- a/softmmu/dirtylimit.c
+++ b/softmmu/dirtylimit.c
@@ -411,13 +411,28 @@ void dirtylimit_set_all(uint64_t quota,
void dirtylimit_vcpu_execute(CPUState *cpu)
{
+ int64_t sleep_us, endtime_us;
+
+ dirtylimit_state_lock();
if (dirtylimit_in_service() &&
dirtylimit_vcpu_get_state(cpu->cpu_index)->enabled &&
cpu->throttle_us_per_full) {
trace_dirtylimit_vcpu_execute(cpu->cpu_index,
cpu->throttle_us_per_full);
- usleep(cpu->throttle_us_per_full);
- }
+ sleep_us = cpu->throttle_us_per_full;
+ dirtylimit_state_unlock();
+ endtime_us = qemu_clock_get_us(QEMU_CLOCK_REALTIME) + sleep_us;
+ while (sleep_us > 0 && !cpu->stop) {
+ if (sleep_us > SCALE_US) {
+ qemu_mutex_lock_iothread();
+ qemu_cond_timedwait_iothread(cpu->halt_cond,
sleep_us / SCALE_US);
+ qemu_mutex_unlock_iothread();
+ } else
+ g_usleep(sleep_us);
+ sleep_us = endtime_us -
qemu_clock_get_us(QEMU_CLOCK_REALTIME);
+ }
+ } else
+ dirtylimit_state_unlock();
}
static void dirtylimit_init(void)
--
2.39.3
--
Best regards
