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[Qemu-devel] [PATCH 8/8] timers: make icount thread-safe
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH 8/8] timers: make icount thread-safe |
Date: |
Tue, 8 Oct 2013 10:47:38 +0200 |
This lets threads other than the I/O thread use vm_clock even in -icount mode.
Signed-off-by: Paolo Bonzini <address@hidden>
---
cpus.c | 42 ++++++++++++++++++++++++++++++++++--------
1 file changed, 34 insertions(+), 8 deletions(-)
diff --git a/cpus.c b/cpus.c
index bc675a4..1e5cba4 100644
--- a/cpus.c
+++ b/cpus.c
@@ -133,7 +133,7 @@ typedef struct TimersState {
static TimersState timers_state;
/* Return the virtual CPU time, based on the instruction counter. */
-int64_t cpu_get_icount(void)
+static int64_t cpu_get_icount_locked(void)
{
int64_t icount;
CPUState *cpu = current_cpu;
@@ -149,6 +149,19 @@ int64_t cpu_get_icount(void)
return qemu_icount_bias + (icount << icount_time_shift);
}
+int64_t cpu_get_icount(void)
+{
+ int64_t icount;
+ unsigned start;
+
+ do {
+ start = seqlock_read_begin(&timers_state.clock_seqlock);
+ icount = cpu_get_icount_locked();
+ } while (seqlock_read_retry(&timers_state.clock_seqlock, start));
+
+ return icount;
+}
+
/* return the host CPU cycle counter and handle stop/restart */
/* cpu_ticks is safely if holding BQL */
int64_t cpu_get_ticks(void)
@@ -246,8 +259,9 @@ static void icount_adjust(void)
return;
}
- cur_time = cpu_get_clock();
- cur_icount = cpu_get_icount();
+ seqlock_write_lock(&timers_state.clock_seqlock);
+ cur_time = cpu_get_clock_locked();
+ cur_icount = cpu_get_icount_locked();
delta = cur_icount - cur_time;
/* FIXME: This is a very crude algorithm, somewhat prone to oscillation.
*/
@@ -265,6 +279,7 @@ static void icount_adjust(void)
}
last_delta = delta;
qemu_icount_bias = cur_icount - (qemu_icount << icount_time_shift);
+ seqlock_write_unlock(&timers_state.clock_seqlock);
}
static void icount_adjust_rt(void *opaque)
@@ -289,10 +304,14 @@ static int64_t qemu_icount_round(int64_t count)
static void icount_warp_rt(void *opaque)
{
- if (vm_clock_warp_start == -1) {
+ /* The icount_warp_timer is rescheduled soon after vm_clock_warp_start
+ * changes from -1 to another value, so the race here is okay.
+ */
+ if (atomic_read(&vm_clock_warp_start) == -1) {
return;
}
+ seqlock_write_lock(&timers_state.clock_seqlock);
if (runstate_is_running()) {
int64_t clock = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
int64_t warp_delta;
@@ -303,14 +322,15 @@ static void icount_warp_rt(void *opaque)
* In adaptive mode, do not let QEMU_CLOCK_VIRTUAL run too
* far ahead of real time.
*/
- int64_t cur_time = cpu_get_clock();
- int64_t cur_icount = cpu_get_icount();
+ int64_t cur_time = cpu_get_clock_locked();
+ int64_t cur_icount = cpu_get_icount_locked();
int64_t delta = cur_time - cur_icount;
warp_delta = MIN(warp_delta, delta);
}
qemu_icount_bias += warp_delta;
}
vm_clock_warp_start = -1;
+ seqlock_write_unlock(&timers_state.clock_seqlock);
if (qemu_clock_expired(QEMU_CLOCK_VIRTUAL)) {
qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
@@ -324,7 +344,10 @@ void qtest_clock_warp(int64_t dest)
while (clock < dest) {
int64_t deadline = qemu_clock_deadline_ns_all(QEMU_CLOCK_VIRTUAL);
int64_t warp = MIN(dest - clock, deadline);
+ seqlock_write_lock(&timers_state.clock_seqlock);
qemu_icount_bias += warp;
+ seqlock_write_unlock(&timers_state.clock_seqlock);
+
qemu_clock_run_timers(QEMU_CLOCK_VIRTUAL);
clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
}
@@ -391,9 +415,11 @@ void qemu_clock_warp(QEMUClockType type)
* you will not be sending network packets continuously instead of
* every 100ms.
*/
+ seqlock_write_lock(&timers_state.clock_seqlock);
if (vm_clock_warp_start == -1 || vm_clock_warp_start > clock) {
vm_clock_warp_start = clock;
}
+ seqlock_write_unlock(&timers_state.clock_seqlock);
timer_mod_anticipate(icount_warp_timer, clock + deadline);
} else if (deadline == 0) {
qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
--
1.8.3.1
- Re: [Qemu-devel] [PATCH 4/8] timers: reorganize icount_warp_rt, (continued)
[Qemu-devel] [PATCH 6/8] timers: introduce cpu_get_clock_locked, Paolo Bonzini, 2013/10/08
[Qemu-devel] [PATCH 7/8] timers: document (future) locking rules for icount, Paolo Bonzini, 2013/10/08
[Qemu-devel] [PATCH 8/8] timers: make icount thread-safe,
Paolo Bonzini <=
Re: [Qemu-devel] [PATCH 0/8] Make icount thread-safe, Andreas Färber, 2013/10/08