On Sun, 2015-11-29 at 10:38 -0500, Meng Xu wrote: > > > 2015-11-29 7:46 GMT-05:00 Yu-An(Victor) Chen <chen...@usc.edu>: > > Hi Meng, > > > Hi, > > > > > So I will rewrite my setup here again, but this time I shorten the > > period and budget for RTDS like you suggested: > > > Nice! :-) > > > > ----------------------------------------------------------------- > > ------------------------------------------------------------ > > > (I like this line, BTW. :-D) > > > > > > for xen-credit : 2vms (both vm are given 8 vCPUs) sharing 8 cores > > (cpu 0-7) using credit scheduler(both with weight of 800 and > > capacity of 400) > > for xen-rtds: 2 vms (both vm are given 8 vCPUs) sharing 8 cores > > (cpu0-7) using RTDS (both with period of 4000(4ms) and budget of > > 2000(2ms))) > > In both setup, dom0 is using 1 core from cpu 8-15 > > > > In both setup: > > > > I loaded VM2 with constant running task with total utilization of 4 > > cores. > > and in VM1 I run iterations of tasks of total utilization rate of 1 > > cores, 2 cores, 3 cores, 4 cores, and then record their > > schedulbility. > > ----------------------------------------------------------------- > > ------------------------------------------------------------ > > > > So st_jobs_stats for the missed deadline jobs are: > > > > trial #1 composed of 2 tasks: total tasks utilization rate = 1 > > > > (period, exe, deadline)=(21ms,12.023ms,21ms) -> miss all deadline > > (period, exe, deadline)=(100ms,37.985ms,100ms) -> no miss > > > yes, this is the information I need and we can solve the mystery > now... > Let's look at this task: > (period, exe, deadline)=(21ms,12.023ms,21ms) -> miss all deadline > Its utilization is 12.023 / 21 ~= 0.5614; > Your VCPU utilization is only 2ms / 4ms = 0.5 > So even when this task is pinned to one VCPU, it will still miss > deadline because it has only one thread. :-) > Mmmm... As I said many times, I don't remember much of all those RT schedulability formulas, but, is really that simple? I mean, if the in- guest scheduling algorithm is global (e.g., global-EDF), the task could migrate, couldn't it?
Is it really the case that you can never schedule tasks with U greater than the smaller U of the various vCPUs (which seems to me to be what you're implying)? Anyway... > So basically, it is because your configuration is incorrect. That's > also why you need to read some literatures in real-time scheduling > theory. ;-) > ... I totally agree with this! ;-D Regards, Dario > -- <<This happens because I choose it to happen!>> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
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