Richard, On Thu, Mar 22, 2007 at 12:10:46PM -0400, Richard C Bilson wrote: > Hello Stephane and others, > > As part of our work on uProfiler we are using perfmon to self-sample > multithreaded programs. Specifically, we have programs with multiple > kernel threads, each with their own perfmon context, each requesting > overflow interrupts through SIGIO. > > The behavior that's troubling me right now is that there appears to be > no guarantee that the SIGIO is delivered to the same kernel thread that > caused the corresponding counter overflow. Specifically, I find our > SIGIO handler being activated on a particular kernel thread with > siginfo's si_fd member referring to the context of a different kernel > thread. > You are perfectly right, POSIX does not stipulate that SIGIO goes to the thread that generated the event. In general asynchronous signals cannot be targeted to a particular thread. I ran into this myself with earlier version of pfmon. There is nothing I can do about it in perfmon. You'd have to structure your code differently or use the trick you are using, i.e., based on the fd forward to the right thread. One thing is sure, is that the signal is not delivered to a thread that blocks the signal. So you could have all but one thread block the signal and then dispatch from there.
> I can understand why this behavior might suit some applications, but it > poses real problems for us: we use overflow notifications as a cue to > sample a variety of bits of application state on that kernel thread, so > getting the notification on a different thread doesn't help us. > > As of now, I haven't been able even to craft an effective work-around. > The best I can come up with is to detect a signal on the "wrong" thread > and respond with a pthread_kill to the right thread. But that seems > like it would significantly increase not only our probe effect but, > more importantly, the time between overflow and sample. > > I hope someone can tell me that there's an obvious switch that I've > overlooked, but I appreciate any comments or ideas. > > Thanks. > -- > Richard C. Bilson, Research Assistant [EMAIL PROTECTED] > http://plg.uwaterloo.ca/~rcbilson > D. R. Cheriton School of Computer Science, University of Waterloo > 200 University Avenue West, Waterloo, Ontario, CANADA N2L 3G1 > _______________________________________________ > perfmon mailing list > [email protected] > http://www.hpl.hp.com/hosted/linux/mail-archives/perfmon/ -- -Stephane _______________________________________________ perfmon mailing list [email protected] http://www.hpl.hp.com/hosted/linux/mail-archives/perfmon/
