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.
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.
Jan
--
Siemens AG, Corporate Technology, CT RDA IOT SES-DE
Corporate Competence Center Embedded Linux
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