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[Qemu-devel] [PULL 16/17] icount: make it thread-safe
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PULL 16/17] icount: make it thread-safe |
Date: |
Thu, 17 Oct 2013 17:48:54 +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 | 37 +++++++++++++++++++++++++++++++------
1 file changed, 31 insertions(+), 6 deletions(-)
diff --git a/cpus.c b/cpus.c
index 6203d98..398229e 100644
--- a/cpus.c
+++ b/cpus.c
@@ -132,7 +132,7 @@ 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;
@@ -148,6 +148,19 @@ 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.vm_clock_seqlock);
+ icount = cpu_get_icount_locked();
+ } while (seqlock_read_retry(&timers_state.vm_clock_seqlock, start));
+
+ return icount;
+}
+
/* return the host CPU cycle counter and handle stop/restart */
/* Caller must hold the BQL */
int64_t cpu_get_ticks(void)
@@ -249,8 +262,9 @@ static void icount_adjust(void)
return;
}
- cur_time = cpu_get_clock();
- cur_icount = cpu_get_icount();
+ seqlock_write_lock(&timers_state.vm_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.
*/
@@ -268,6 +282,7 @@ static void icount_adjust(void)
}
last_delta = delta;
qemu_icount_bias = cur_icount - (qemu_icount << icount_time_shift);
+ seqlock_write_unlock(&timers_state.vm_clock_seqlock);
}
static void icount_adjust_rt(void *opaque)
@@ -292,10 +307,14 @@ 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.vm_clock_seqlock);
if (runstate_is_running()) {
int64_t clock = qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
int64_t warp_delta;
@@ -306,14 +325,15 @@ 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.vm_clock_seqlock);
if (qemu_clock_expired(QEMU_CLOCK_VIRTUAL)) {
qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
@@ -327,7 +347,10 @@ 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.vm_clock_seqlock);
qemu_icount_bias += warp;
+ seqlock_write_unlock(&timers_state.vm_clock_seqlock);
+
qemu_clock_run_timers(QEMU_CLOCK_VIRTUAL);
clock = qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL);
}
@@ -391,9 +414,11 @@ void qemu_clock_warp(QEMUClockType type)
* you will not be sending network packets continuously instead of
* every 100ms.
*/
+ seqlock_write_lock(&timers_state.vm_clock_seqlock);
if (vm_clock_warp_start == -1 || vm_clock_warp_start > clock) {
vm_clock_warp_start = clock;
}
+ seqlock_write_unlock(&timers_state.vm_clock_seqlock);
timer_mod_anticipate(icount_warp_timer, clock + deadline);
} else if (deadline == 0) {
qemu_clock_notify(QEMU_CLOCK_VIRTUAL);
--
1.8.3.1
- [Qemu-devel] [PULL 10/17] timer: extract timer_mod_ns_locked and timerlist_rearm, (continued)
- [Qemu-devel] [PULL 10/17] timer: extract timer_mod_ns_locked and timerlist_rearm, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 11/17] timer: add timer_mod_anticipate and timer_mod_anticipate_ns, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 07/17] timer: protect timers_state's clock with seqlock, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 06/17] seqlock: introduce read-write seqlock, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 08/17] qemu-thread: add QemuEvent, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 12/17] icount: use cpu_get_icount() directly, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 09/17] timer: make qemu_clock_enable sync between disable and timer's cb, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 15/17] icount: document (future) locking rules for icount, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 13/17] icount: reorganize icount_warp_rt, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 14/17] icount: prepare the code for future races in calling qemu_clock_warp, Paolo Bonzini, 2013/10/17
- [Qemu-devel] [PULL 16/17] icount: make it thread-safe,
Paolo Bonzini <=
- [Qemu-devel] [PULL 17/17] exec: remove qemu_safe_ram_ptr, Paolo Bonzini, 2013/10/17