On 29.07.20 05:28, Peng Fan wrote:
Subject: Re: jailhouse jitter?
On 27.07.20 08:56, Peng Fan wrote:
Subject: Re: jailhouse jitter?
On 27.07.20 08:25, Peng Fan wrote:
Hi Jan
...
I tested the SDEI on i.MX8MM, it shows the jitter became smaller.
Without SDEI, the gic-demo jitter is 999ns+ With SDEI, the gic-demo
jitter is 124ns~246ns.
Indeed no more vmexits.
But the max jitter, some times SDEI bigger only when program start
up,
mostly because of CACHE WARM UP I think.
That is one source. If you add a warm-up period, they can be
mitigated, though.
The other source might be last-level cache sharing. If there are
cache-miss counters, maybe you can check if those increase along the
peaks.
Yes. When I add stress-ng in root cell, the jitter became larger sometimes.
I've seen the same on the ultra96. My cache theory should be validated,
though, because I would have assumed that all of the gic demo fits into a
core-local cache.
After thinking more about root cell color, when booting jailhouse before Linux.
We are not using 1:1 mapping anymore or we could use 1:1 mapping with many
pieces of small ram area.
I suspect Linux may not like a device tree with hundreds or thousands of
memory region entries.
So I think the first 1 is better, but when use kmalloc for dma usage sometimes,
it will bring issues, because not 1:1 mapping, unless we let all drivers use
dedicated dma area reserved and not colored.
We will need an SMMU for colored Linux instances. That will make things
appear 1:1 mapped again for Linux.
Will you move SDEI support to jailhouse mainline?
Once the to-dos are addressed. Any contributions?
I'll read more into your patches and check the to-dos you listed in
the jailhouse commit log to see what I could help there.
Item one (SDEI probing) is almost resolved.
BTW, did you have to patch ATF for your experiment? Will you upstream
that patch?
Yes. I'll upstream that. Quite simple, I only enabled one SDEI private event.
Perfect.
Sent out.
https://review.trustedfirmware.org/c/TF-A/trusted-firmware-a/+/5116
Great! Let's see how the review works out, then I could try getting my
patches ready for upstream as well.
Jan
--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux
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