On Mon, Jul 29, 2013 at 2:26 PM, Paolo Bonzini <pbonz...@redhat.com> wrote:
> Il 29/07/2013 05:16, Liu Ping Fan ha scritto:
>> In kvm mode, vm_clock may be read on AioContexts outside BQL(next
>> patch). This will make timers_state --the foundation of vm_clock
>> exposed to race condition. Using private lock to protect it.
>> Note in tcg mode, vm_clock still read inside BQL, so icount is
>> left without change.
>>
>> Lock rule: private lock innermost, ie BQL->"this lock"
>
> This is quite expensive; on the other hand it is probably a good thing
> to do even without the other patches.
>
> Can you use the seqlock primitive we initially worked on for the memory
> dispatch (with the BQL on the write side)?
>
Fine, of course, seqlock is a better one.
Thanks,
Pingfan
> Paolo
>
>> Signed-off-by: Liu Ping Fan <pingf...@linux.vnet.ibm.com>
>> ---
>> cpus.c | 26 +++++++++++++++++++++-----
>> 1 file changed, 21 insertions(+), 5 deletions(-)
>>
>> diff --git a/cpus.c b/cpus.c
>> index 61e86a8..4af81e9 100644
>> --- a/cpus.c
>> +++ b/cpus.c
>> @@ -112,7 +112,9 @@ typedef struct TimersState {
>> int64_t dummy;
>> } TimersState;
>>
>> -TimersState timers_state;
>> +static TimersState timers_state;
>> +/* lock rule: innermost */
>> +static QemuMutex timers_state_lock;
>>
>> /* Return the virtual CPU time, based on the instruction counter. */
>> int64_t cpu_get_icount(void)
>> @@ -134,11 +136,14 @@ int64_t cpu_get_icount(void)
>> /* return the host CPU cycle counter and handle stop/restart */
>> int64_t cpu_get_ticks(void)
>> {
>> + int64_t ret;
>> +
>> if (use_icount) {
>> return cpu_get_icount();
>> }
>> + qemu_mutex_lock(&timers_state_lock);
>> if (!timers_state.cpu_ticks_enabled) {
>> - return timers_state.cpu_ticks_offset;
>> + ret = timers_state.cpu_ticks_offset;
>> } else {
>> int64_t ticks;
>> ticks = cpu_get_real_ticks();
>> @@ -148,41 +153,51 @@ int64_t cpu_get_ticks(void)
>> timers_state.cpu_ticks_offset += timers_state.cpu_ticks_prev -
>> ticks;
>> }
>> timers_state.cpu_ticks_prev = ticks;
>> - return ticks + timers_state.cpu_ticks_offset;
>> + ret = ticks + timers_state.cpu_ticks_offset;
>> }
>> + qemu_mutex_unlock(&timers_state_lock);
>> + return ret;
>> }
>>
>> /* return the host CPU monotonic timer and handle stop/restart */
>> int64_t cpu_get_clock(void)
>> {
>> int64_t ti;
>> +
>> + qemu_mutex_lock(&timers_state_lock);
>> if (!timers_state.cpu_ticks_enabled) {
>> - return timers_state.cpu_clock_offset;
>> + ti = timers_state.cpu_clock_offset;
>> } else {
>> ti = get_clock();
>> - return ti + timers_state.cpu_clock_offset;
>> + ti += timers_state.cpu_clock_offset;
>> }
>> + qemu_mutex_unlock(&timers_state_lock);
>> + return ti;
>> }
>>
>> /* enable cpu_get_ticks() */
>> void cpu_enable_ticks(void)
>> {
>> + qemu_mutex_lock(&timers_state_lock);
>> if (!timers_state.cpu_ticks_enabled) {
>> timers_state.cpu_ticks_offset -= cpu_get_real_ticks();
>> timers_state.cpu_clock_offset -= get_clock();
>> timers_state.cpu_ticks_enabled = 1;
>> }
>> + qemu_mutex_unlock(&timers_state_lock);
>> }
>>
>> /* disable cpu_get_ticks() : the clock is stopped. You must not call
>> cpu_get_ticks() after that. */
>> void cpu_disable_ticks(void)
>> {
>> + qemu_mutex_lock(&timers_state_lock);
>> if (timers_state.cpu_ticks_enabled) {
>> timers_state.cpu_ticks_offset = cpu_get_ticks();
>> timers_state.cpu_clock_offset = cpu_get_clock();
>> timers_state.cpu_ticks_enabled = 0;
>> }
>> + qemu_mutex_unlock(&timers_state_lock);
>> }
>>
>> /* Correlation between real and virtual time is always going to be
>> @@ -353,6 +368,7 @@ static const VMStateDescription vmstate_timers = {
>>
>> void configure_icount(const char *option)
>> {
>> + qemu_mutex_init(&timers_state_lock);
>> vmstate_register(NULL, 0, &vmstate_timers, &timers_state);
>> if (!option) {
>> return;
>>
>
