Messages in this thread |  | | | Date | Fri, 14 Oct 2005 05:45:14 +0200 | | From | Ingo Molnar <> | | Subject | Re: 1.6ms jitter in rtc_wakeup (Re: 2.6.14-rc4-rt1) |
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* Esben Nielsen <simlo@phys.au.dk> wrote:
> I set up rtc_wakeup and got a jitter up 1.6ms! > It came when I cd'en into a nfs-mount and typed ls.
> ls-11239 0Dn.. 4us : profile_hit (__schedule) > ls-11239 0Dn.1 4us : sched_clock (__schedule) > ls-11239 0Dn.1 5us : check_tsc_unstable (sched_clock) > ls-11239 0Dn.1 5us : tsc_read_c3_time (sched_clock) > IRQ 8-775 0D..2 6us : __switch_to (__schedule) > IRQ 8-775 0D..2 7us!: __schedule <ls-11239> (75 0) > IRQ 8-775 0...1 1594us : trace_stop_sched_switched (__schedule) > IRQ 8-775 0D..2 1594us : trace_stop_sched_switched <IRQ 8-775> (0 0) > IRQ 8-775 0D..2 1595us : trace_stop_sched_switched (__schedule)
ouch! This very much looks like a hardware induced latency, because the codepath from those two __schedule points is extremely short and there is no loop there. Have you tested this particular box before too? If not, can you reproduce this latency with older versions of -rt too on the same box, or is this completely new? Occasionally there are boxes that show clear signs of hardware latencies - there's little the kernel can do about those.
Wild shot in the dark: are there any power-saving modes enabled on the box? Another shot in the dark: can you trigger these latencies if the networking card is ifconfig down-ed? I.e. perhaps it's related to DMA done by the networking device. Playing with BIOS settings / DMA/PCI priorities might help reduce DMA related latencies ...
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