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SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U9.3
Date
>i have released the -U9.3 Real-Time Preemption patch, ...
>
It is getting hard to keep up with the updates....

This version built OK and since I noticed it includes fixes for the
parallel port, I added that back to my configuration and built / booted
without any problems. I still see the BUG from:

Oct 22 12:27:50 dws77 kernel: 8139too Fast Ethernet driver 0.9.27
Oct 22 12:27:50 dws77 kernel: eth0: RealTek RTL8139 at 0xdc00,
00:50:bf:39:11:fc, IRQ 11
Oct 22 12:27:50 dws77 kernel: BUG: atomic counter underflow at:
Oct 22 12:27:50 dws77 kernel: [<c02b8f88>] qdisc_destroy+0x98/0xa0 (12)

I saw the messages about fixes for the other network drivers, but
don't forget this one.

Real time stress tests ran more smoothly this time with fewer
odd symptoms but a few new symptoms showed up too. I'll send the
boot log and traces separately. The following summarizes the tests
and results.

[1] X11 stress - very clean, max CPU delay was only 20 usec.

[2] proc stress - very clean, max CPU delay was only 30 usec.

[3] network output stress - only trace much worse than U9.2. An odd
pattern in the graph showing a delay of roughly 400 usec every 5
seconds with a much smaller delay following. There were also a couple
bursts of delays at 90-100 seconds, and 250-260 seconds. Did not
see this pattern on any other test.

[4] network input stress - very clean, max CPU delay was only 80 usec.

[5] disk write stress - very clean, max CPU delay only 70 usec.

[6] disk copy stress - very clean, max CPU delay only 90 usec.

[7] disk read stress - first 25 seconds, had a pattern of roughly 100 usec
CPU delays with a few peaks at 500 usec. After that, was very clean, almost
99.7% of the CPU delays were under 100 usec.

During these tests (total 25-30 minutes) had seven latency traces
over >200 usec. Summary follows:

00 - find_symbol, a single trace line over 400 usec as follows
preemption latency trace v1.0.7 on 2.6.9-rc4-mm1-RT-U9.3
-------------------------------------------------------
latency: 495 us, entries: 9 (9) | [VP:1 KP:1 SP:1 HP:1 #CPUS:2]
-----------------
| task: modprobe/3643, uid:0 nice:-10 policy:0 rt_prio:0
-----------------
=> started at: _spin_lock_irqsave+0x1f/0x80 <c0314f4f>
=> ended at: _spin_unlock_irq+0x1b/0x40 <c031538b>
=======>
00000001 0.000ms (+0.000ms): _spin_lock_irqsave (resolve_symbol)
00000001 0.000ms (+0.447ms): __find_symbol (resolve_symbol)
00010001 0.448ms (+0.000ms): do_nmi (__find_symbol)
00010001 0.448ms (+0.000ms): do_nmi (add_preempt_count)
00010001 0.449ms (+0.042ms): do_nmi (<00200093>)
00000001 0.491ms (+0.000ms): use_module (resolve_symbol)
00000001 0.492ms (+0.001ms): already_uses (use_module)
00000001 0.493ms (+0.000ms): kmem_cache_alloc (use_module)
00000001 0.494ms (+0.000ms): _spin_unlock_irq (resolve_symbol)
01, 02, 03, 05, 06 - flush_tlb
latency: 1815 us, entries: 108 (108) | [VP:1 KP:1 SP:1 HP:1 #CPUS:2]
latency: 8959 us, entries: 180 (180) | [VP:1 KP:1 SP:1 HP:1 #CPUS:2]
latency: 175300 us, entries: 4000 (8116) | [VP:1 KP:1 SP:1 HP:1
#CPUS:2]
latency: 80679 us, entries: 1545 (1545) | [VP:1 KP:1 SP:1 HP:1
#CPUS:2]
latency: 76801 us, entries: 3561 (3561) | [VP:1 KP:1 SP:1 HP:1
#CPUS:2]
This is that symptom I reported before where something gets "stuck"
and one or more clock ticks later, it finally gets freed up. Note that
the real time application did not see any of these delays. It may
be interesting to do another test w/ two real time tasks to see if
these are real or a sampling artifact.

04 - avc_insert, a single > 200 usec trace entry.
preemption latency trace v1.0.7 on 2.6.9-rc4-mm1-RT-U9.3
-------------------------------------------------------
latency: 216 us, entries: 4 (4) | [VP:1 KP:1 SP:1 HP:1 #CPUS:2]
-----------------
| task: fam/2933, uid:0 nice:0 policy:0 rt_prio:0
-----------------
=> started at: _spin_lock_irqsave+0x1f/0x80 <c0314f4f>
=> ended at: _spin_unlock_irqrestore+0x20/0x50 <c0315340>
=======>
00000001 0.000ms (+0.000ms): _spin_lock_irqsave (avc_has_perm_noaudit)
00000001 0.000ms (+0.214ms): avc_insert (avc_has_perm_noaudit)
00000001 0.214ms (+0.000ms): memcpy (avc_has_perm_noaudit)
00000001 0.215ms (+0.000ms): _spin_unlock_irqrestore (avc_has_perm_noaudit)
--Mark

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