rusage and pthreads
materribile at yahoo.com
Wed Jan 19 01:01:18 UTC 2011
> > I'm trying to figure out the interactions between
> rusage and pthreads.
> There largely isn't any-- struct rusage is per-process, not
> per thread.
> > Peeking around in the kernel (7.2) I see updates
> occurring in various places. kern_clock.c, for
> instance, appears to increment the memory occupancy (*rss)
> counters. This would make it appear that every thread
> gets part of the count, but also that only the process that
> happens to have the CPU at that moment gets its count
> updated, even if it holds the memory. Am I misreading
> Nope. statclock() is fired off periodically (with
> some fuzz, to avoid clever games by processes trying to
> avoid being sampled) to update the stats for the currently
> running process.
> > And the context switch counters also appear to be
> updated per-thread, but in mi_switch(), in
> kern_synch.c. Is this true?
> > If the answer is "yes, it's per-thread", then how does
> a process report its usages without putting the requisite
> code in each thread, along with the machinery to divert from
> whatever the thread is doing (even waiting on I/O) to get
> the report at (nearly) the same time in all threads?
> The process doesn't have userland threads updating this
> information. The kernel keeps track of it, and it
> updates the information periodically when the scheduler does
> context switches, when statclock() fires off, when disk I/O
> completes, etc.
I'm looking at kern_clock.c::statclock(int usermode)
The code in question begins
struct rusage* ru;
struct vmspace* vm;
struct thread *td;
struct proc *p;
td = curthread;
p = td->td_proc;
and continues further down
ru = &td->td_ru;
ru->ru_ixrss += pgtok(vm->vm_tsize);
ru->ru_idrss += pgtok(vm->vm_dsize);
ru->ru_isrss += pgtok(vm->vm_ssize);
This looks to me like it's accumulating the data in per-thread counters. What's more, it's consistent with what I'm seeing on the user side. Note that this is 7.2; if 8.x behaves differently I'd like to know.
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