Messages in this thread | | | Subject | Re: [patch] voluntary-preempt-2.6.8.1-P0 | From | Lee Revell <> | Date | Sun, 15 Aug 2004 22:43:41 -0400 |
| |
On Sun, 2004-08-15 at 22:36, Ingo Molnar wrote: > * Lee Revell <rlrevell@joe-job.com> wrote: > > > There are a number of samples above 700us. I am working with a period > > time of 666 usecs, and since there are 2 periods per buffer, we would > > have to hit two > 666 usec latencies in a row for an xrun - it appears > > that there are many individual latencies above 666, certainly more > > than there are xruns. So, maybe the mlockall issue is not a result of > > triggering a single large latency, but of increasing the frequency of > > these higher latencies so that we are more likely to hit 2 in a row. > > hm, it seems the mlockall() issue is too deterministic for it to be a > statistical-only phenomenon. Also, isnt that xrun on the order of 15 > msecs? That's way too big too. >
I believe the constant-time behavior that I reported was an artifact of ALSA xrun debugging. Now it seems like the latency produced *does* correspond directly to the amount of memory being mlockall'ed. If ./mlockall-test 1500 triggers an xrun at all it's ~0.2ms. 3000 triggers a ~1ms xrun, and 10000 a ~3 ms xrun.
> > IIRC ksoftirqd will defer more work under load, and ksoftirqd is one > > of the more common offenders to hit the extract_entropy latency. > > Maybe mlockall causes more softirqs to be deferred, thus increaing the > > change that we will have to do more than 666 usecs worth of work on 2 > > successive wakeups. > > there should be no relation between softirqs and mlockall(). > > this is truly a mind-boggling latency. mlockall() is fully preemptible. > All it does is to pre-fault the whole range of pages that a process has. > > could you try another thing: modify mlockall-test.cc to use mlock() on > the freshly allocated anonymous pages? Does this produce the same > latencies? mlockall() prefaults _all_ pages the process currently has. > Maybe mlockall() touches some page that is mapped both by jackd and > mlockall-test and thus somehow interacts with jackd's scheduling. >
I don't know C++, Florian wrote this program. Can you provide a pseudo-patch?
> the anonymous pages themselves can have no IPC-alike connection to any > page jackd owns. It is unlikely for that to be any connection between > jackd and mlockall-test - other than both map glibc. To further exclude > any possibility of resource sharing between jackd and mlockall-test, > could you compile the later with -static?
Sure, I will try this.
Lee
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |