Fusion and RT Rreempt [Was: RTAI/fusion 0.7.2]

[Max Krasnyansky]

Gilles Chanteperdrix wrote:
> Max Krasnyansky wrote:
>  > Yeah, but result from my app does not look very good, does it ?
>  > I mean 36.8 usec from kernel task to user task. There is also about 5 usec
>  > worst case interrupt dispatch latency (measured long time ago with oscope).
>  > So the total is more than 40 usec to propagate interrupt into the user-space.
>  > Remember when you and Paolo said that you're seeing 15 usec worst case
>  > latency. I said that it's with the timer compensation and stuff, actual
>  > interrupt response time is much worse.
> 
> Timer compensation is less than 10us. The rest of the difference
> could conceivably come from the fact that the latency test has a 100us
> period whereas your external interrupt is triggered every 4ms, which
> would cause disastrous cache effect.
> 
> What happens if you run the latency test with a 4ms period?
> 
Quick test (latency -p 4000 + network load + IDE load) shows
RTS|        2249|        7150|       23975|       0|    00:04:15/00:04:15

So you are right. It seems like it's cache related.

----
Here is something even more interesting.
I just ran the same test on the IBM Z-Pro machine:

model name      : Intel(R) Xeon(TM) CPU 3.60GHz
stepping        : 1
cpu MHz         : 3601.003
cache size      : 1024 KB

00:00.0 Host bridge: Intel Corp. E7525 Memory Controller Hub (rev 0c)
00:02.0 PCI bridge: Intel Corp. E7525/E7520/E7320 PCI Express Port A 	(rev 0c)
00:03.0 PCI bridge: Intel Corp. E7525/E7520/E7320 PCI Express Port A1 (rev 0c)
00:04.0 PCI bridge: Intel Corp. E7525/E7520 PCI Express Port B (rev 0c)
[snip]
01:00.0 Ethernet controller: Broadcom Corporation NetXtreme BCM5721 Gigabit 
Ethernet PCI Express (rev 11)

2.6.11, adeos r10, fusion CVS.

latency -p 100 + high network load
RTS|         343|       13153|       51667|       0|    00:02:30/00:02:30

latency -p 4000 + high network load
RTS|        1262|      780892|     1724248|       0|    00:00:19/00:00:19

How about that :) ? 1.7 milliseconds. Wow.
This is totally reproduceable btw. I played with the BIOS settings and stuff,
makes no difference. MSI workaround is enabled but makes no difference.

I was wondering what kind of numbers are you guys seeing on IA64 machines ?

Max