[Qemu-devel] [PATCH 8/8] timers: make icount thread-safe

2013-10-08 Thread Paolo Bonzini 
This lets threads other than the I/O thread use vm_clock even in -icount mode.

Signed-off-by: Paolo Bonzini pbonz...@redhat.com
---
 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 8/8] timers: make icount thread-safe

2013-10-08 Thread Alex Bligh 

On 8 Oct 2013, at 09:47, Paolo Bonzini wrote:

 This lets threads other than the I/O thread use vm_clock even in -icount mode.
 
 Signed-off-by: Paolo Bonzini pbonz...@redhat.com

Looks good to me

Alex

 ---
 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
 
 
 

-- 
Alex Bligh