Messages in this thread | | | Date | Mon, 26 Jul 2004 14:40:59 +0200 | From | Ingo Molnar <> | Subject | Re: [patch] voluntary-preempt-2.6.8-rc2-J3 |
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* Lee Revell <rlrevell@joe-job.com> wrote:
> > > Yes, jackd does exactly this, mlockall then opens the ALSA driver with > > > mmap. > > > > ok, i fixed this in -J3: > > > > http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.8-rc2-J3 > > > > -J3 also includes a number of softirq latency fixes for the networking > > layer. > > OK, I will try this. I have not seen any latency issues with softirqs > with -I4. [...]
i'm going through the subsystems systematically and i'm stressing them beyond normal use. These networking latencies need a high number of in flight packets, multiple TCP sockets, and a 100 mbit link or faster. (this is a more common workload on a corporate desktop, but not typical on a home desktop.)
> [...] Other than the few remaining hot spots, the only thing that > triggers latencies over 100 usecs during normal operation is the IDE > I/O completion, which can be easily controlled by lowering the max SG > size.
ok, i'll take a look whether there's a way to control this without having to artificially impact the IO patterns.
> Here is one that I think happens when deleting a large number of > files, or a directory that had a large number of files. Specifically, > this happens when bonnie exits. > > Jul 25 20:25:36 mindpipe kernel: > > [...] 16ms non-preemptible critical section violated 1 ms preempt > threshold starting at select_parent+0x18/0xd0 and ending at > select_parent+0x94/0xd0
ok, this should be the dcache/icache zapping. I've done some latency reduction in this area but apparently not enough.
> I am also seeing a lot of shorter timing violations that involve > unmap_vmas. Not sure what triggers this one.
it might just be a common operation, being hit by the IDE hardirq latency. (which thus is added to the 'scheduling' latency.) Although none of the traces show IDE hardirq leftovers [but they might be cleared from the stack by the time we notice the latency.]
Can you see these 1-2 msec latencies even if you reduce the IDE sg-size drastically via the max_sectors tunable? (just for testing purposes, to eliminate hardirq latencies as much as possible)
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