Messages in this thread |  | | Subject | Re: [patch] voluntary-preempt-2.6.8.1-P2 | From | Thomas Charbonnel <> | Date | Tue, 17 Aug 2004 13:26:14 +0200 |
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Ingo Molnar wrote : > here's -P2: > > http://redhat.com/~mingo/voluntary-preempt/voluntary-preempt-2.6.8.1-P2 > > Changes since -P1: > > - trace interrupted kernel code (via hardirqs, NMIs and pagefaults) > > - yet another shot at trying to fix the IO-APIC/USB issues. > > - mcount speedups - tracing should be faster > > Ingo
I think I stumbled across some bugs/false positives. Those tests were run with acpi=off, so that this specific issue doesn't interfere. voluntary_preemption is set to 3 throughout.
The first problem was already reported by Lee Revell. Creating a new tab in gnome-terminal gives :
[...] 0.064ms (+0.000ms): preempt_schedule (try_to_wake_up) 0.065ms (+0.000ms): preempt_schedule (copy_page_range) 0.065ms (+0.000ms): preempt_schedule (copy_page_range) [... plenty of preempt_schedule (copy_page_range) skipped ...] 0.202ms (+0.000ms): preempt_schedule (copy_page_range) 0.202ms (+0.000ms): preempt_schedule (copy_page_range) 0.202ms (+0.000ms): check_preempt_timing (touch_preempt_timing)
This is induced by kernel_preemption=0 and disappears with kernel_preemption=1. It seems to be a side-effect of the current design. Is there a way to avoid this ?
The second one still involves creating a new tab in gnome-terminal, but with kernel_preemption=1 :
preemption latency trace v1.0 ----------------------------- latency: 130 us, entries: 6 (6) process: gnome-terminal/14381, uid: 1000 nice: 0, policy: 0, rt_priority: 0 =======> 0.000ms (+0.000ms): __vma_link_rb (copy_mm) 0.000ms (+0.000ms): rb_insert_color (copy_mm) 0.000ms (+0.000ms): __rb_rotate_left (rb_insert_color) 0.000ms (+0.000ms): copy_page_range (copy_mm) 0.000ms (+0.000ms): pte_alloc_map (copy_page_range) 0.127ms (+0.126ms): check_preempt_timing (touch_preempt_timing)
When entering check_preempt_timing, preempt_thresh was 0, and preempt_max_latency had been freshly reset to 100. It should have triggered this code : if (latency < preempt_max_latency) goto out; but for some reason it didn't (or there is a problem in the tracing code, not showing events that would have increased 'latency').
Thomas
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