Alexandra (Sasha) Fedorova wrote: > I am writing some code that will be called from the function ts_tick(), which > is called by clock_tick(). Comments in ts_tick() say that when one releases a > thread lock s/he should use "thread_unlock_nopreempt()" since "clock thread > cannot be pre-empted". (See > http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/disp/ts.c, > line 1781). > > My question is, if my code is called from ts_tick(), can I not acquire any > adaptive mutexes? I thought that I cannot use MUTEX_ADAPTIVE (MUTEX_DEFAULT) > mutex, because it might block, and, according to those comments, the thread > executing clock_tick cannot be blocked. Adaptive mutexes are aquired in the clock thread's context. The clock thread can block (for example, in trying to grab a lock that's already held), but that's different from being preempted (which could happen when dropping a thread lock (see the implementation of disp_lock_exit()).
> So I was going to use MUTEX_SPIN. And then, I went through > clock_tick_process(), a function that calls clock_tick() (see > http://cvs.opensolaris.org/source/xref/onnv/onnv-gate/usr/src/uts/common/os/clock_tick.c) > and saw that it acquires an adaptive mutex: > > 367 plockp = t->t_plockp; > 368 mutex_enter(plockp); > Right. > I haven't found any place where plockp (or the p_lock mutex to which it > points) was initialized, so I assume it's adaptive. > The thread is referencing the p_lock in the process structure (proc_t). I don't see any explicit initialization of that lock (other than being bzero()ed)....but yes, it's adaptive. > Could you please shed some light on this issue? Is it safe to use an adaptive > mutex in the code called from clock_tick? Yes. It's safe...you probably just want to keep in mind the possibility that clock might back up, if the mutexes it needs to get it's job done are contended....which in general can be "painful" for the system. :) Thanks, -Eric _______________________________________________ opensolaris-code mailing list opensolaris-code@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/opensolaris-code
