Re: [libvirt] [PATCH v3 1/2] Implement the asynchronous suspend and RTC wakeup

On 11/09/2011 05:05 AM, Srivatsa S. Bhat wrote: > Add the core functions that implement the functionality of the API. > Suspend is done by using an asynchronous mechanism so that we can return > the status to the caller successfully before the host gets suspended. This > asynchronous operation is achieved by suspending the host in a separate > thread of execution. > > +

> + return -1; > + > + setAlarmCmd = virCommandNewArgList("rtcwake", "-m", "no", "-s", NULL); > + virCommandAddArgFormat(setAlarmCmd, "%lld", alarmTime); 'man rtcwake' says that not all systems support RTC wake from S4; systems that have a functioning nvram-wakeup will succeed, but that is not all systems. Do we need to be more cautious about allowing S4 suspension if we can't prove that RTC will wake up the system from S4? On the other hand, you are using -m no to just set the wakeup time, which ought to fail if the system does not support the requested delay or the ability to wake up, so that you never actually suspend until after you know the wakeup was successfully scheduled. Hmm, does that mean the public API should provide a way to schedule the wakeup without also scheduling a suspend?

> +++ b/src/util/threads-pthread.c > @@ -81,10 +81,25 @@ void virMutexDestroy(virMutexPtr m) > pthread_mutex_destroy(&m->lock); > } > > -void virMutexLock(virMutexPtr m){ > +void virMutexLock(virMutexPtr m) > +{ > pthread_mutex_lock(&m->lock); > } > > +/** > + * virMutexTryLock: I'm not convinced we need this. As I understand it, your code does: thread 1: thread 2: thread 3: request suspend grab lock spawn helper sleep 10 sec return success request suspend lock not available return failure suspend resume request suspend lock not available return failure release lock But we don't need a try-lock operation, if we do: thread 1: thread 2: thread 3: request suspend grab lock request suspend mark flag to true release lock grab lock flag already true release lock return failure spawn helper sleep 10 sec return success suspend resume grab lock flag already true release lock return failure grab lock clear flag release lock That is, instead of holding the lock for the entire duration of the suspend, just hold the lock long enough to mark a volatile variable; then you no longer need a non-blocking try-lock primitive, because the lock will never starve anyone else long enough to be an issue.