Re: [patch] voluntary-preempt-2.6.8-rc2-M5

Lee Revell
2004-08-01T18:07:52Z

On Sun, 2004-08-01 at 07:28, Ingo Molnar wrote:
> On Fri, 30 Jul 2004, Lee Revell wrote:
>
> > Results with 2.6.8-rc2-M5:
> >
> > Configuration max usecs
> > -----------------------------------------------------------------
> > All IRQs threaded 370
> > Soundcard IRQ not threaded 335
> > Soundcard IRQ not threaded + max_sectors_kb -> 64 161
> >
> > So, it looks like the added configurability does add some overhead - 161
> > usecs vs. 50. [...]
>
> +110 usecs is too much to be explained by redirection and configurability
> overhead. The configurability overhead is near zero.
>
> could you try to repeat the '50 usecs' test with -L2 [that was the one you
> used?] to make sure it's repeatable? The latencies of -L2 and -M5 should
> be near identical. The configurability should at most cause a 1-2 usecs
> overhead - definitely not two orders of magnitude higher. So if there's a
> difference then i must have degraded one of the latency reduction changes
> between L2 and M5.

The above numbers really do not tell you much, I have some better ones.
Here is the histogram for a 5,000,000 sample run with M5:

Delay Count
----- -----
6 98189
7 2013275
8 51025
9 120465
10 93339
11 72087
12 116165
13 106433
14 85930
15 57178
16 59835
17 51096
18 71671
19 106738
20 109491
21 84906
22 2215
23 946
24 1755
25 1977
26 1589
27 1117
28 1889
29 1616
30 1858
31 2926
32 3111
33 2558
34 400
35 1366
36 2172
37 2840
38 1088
39 1042
40 172
41 26
42 32
43 43
44 41
45 10
46 8
47 36
48 109
49 125
50 83
51 45
52 36
53 7
55 1
56 1
58 1
61 1
62 1
68 1
75 1
77 1
79 1
89 1
97 1

So if you discard the highest ~10 of 5,000,000, it's the same as L2. Maybe a
corner case, or a new race condition? I will run the above test with L2.

I wonder if the multiple spikes represent different code paths, or the same
but with a hot/warm/cold cache?

Lee