Fusion and RT Rreempt [Was: RTAI/fusion 0.7.2]
maxk at qualcomm.com
Thu Jun 2 02:49:56 CEST 2005
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)
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 ?
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