Hi Meng, So I will rewrite my setup here again, but this time I shorten the period and budget for RTDS like you suggested: -----------------------------------------------------------------------------------------------------------------------------
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 trial #2 composed of 2 tasks: total tasks utilization rate = 1 (period, exe, deadline)=(68ms,40.685ms,68ms) -> miss all deadline (period, exe, deadline)=(70ms,28.118ms,70ms) -> no miss trial #3 composed of 2 tasks: total tasks utilization rate = 1 (period, exe, deadline)=(16ms,11.613ms,16ms) -> miss all deadline (period, exe, deadline)=(46ms,12.612ms,46ms) -> no miss I do notice that for within the task that misses deadline, the completion time get progressively longer, for example: for trial #3, a snapshot of the task st_jobs_stats tells me that the completion time of the job is 79ms and then 87ms, and then 95ms ok, I will look into the reference you provide, I just started my research in the rt fields, there is still a lot for me to learn. Thank you again for reply! Thank you! On Sat, Nov 28, 2015 at 7:09 AM, Meng Xu <xumengpa...@gmail.com> wrote: > 2015-11-28 7:20 GMT-05:00 Yu-An(Victor) Chen <chen...@usc.edu>: > > Hi Meng, > > > > Thank you so much for being this patience. > > > > So a task set is composed of a collection of real-time tasks, and each > > real-time task is a sequence of jobs that are released periodically... > All > > jobs are periodic, where each job Ti is defined by a period (and > deadline) > > pi and a worse-case execution time ei, with pi ≥ ei ≥ 0 and pi, ei ∈ > > integers. Each job is comprised of a number of iterations of floating > point > > operations during each job. This is based on the base task.c provided > with > > the LITMUSRT userspace library. > > I knew this information. Basically, I did the experiment with this > kind of configuration before. What I want to know is what is the range > of period, execution and deadline you have for the taskset and when a > taskset is unschedulable under your experiment, what is the > st_jobs_stats result from the LITMUS which will show which job of > which task misses deadline. If you try to service a task with period = > 100, exe = 50, deadline = 100, specificed as (100, 50, 100), with a > VCPU with period = 100 and budget = 100, you will never schedule this > task. The reason is because the VCPU can be unavailable when task is > released. > A theoretical analysis can be found in this paper "Periodic Resource > Model for Compositional RealTime Guarantees" > > http://repository.upenn.edu/cgi/viewcontent.cgi?article=1033&context=cis_reports > > BTW, I'm assuming you are familiar with the schedulability test for > real time systems since you are talking about schedulability. If my > assumption is wrong, you should have a look at the survey paper A > survey of hard real-time scheduling for multiprocessor systems > (http://dl.acm.org/citation.cfm?id=1978814). This will at least tell > you when you should expect a taskset is schedulable in theory. If a > taskset is claimed unschedulabled in theory, it is very likely > unscheduble in practice. In addition, it will tell you taskset > utilization is not the only factor that affects the schedulablity. > Other factors, such as the highest taks utilization in a taskset, > scheduling algorithm, task period relation, can affect schedulability > also. > > Best, > > Meng > > > > > > > > On Fri, Nov 27, 2015 at 4:17 PM, Meng Xu <xumengpa...@gmail.com> wrote: > >> > >> 2015-11-27 14:50 GMT-05:00 Yu-An(Victor) Chen <chen...@usc.edu>: > >> > Hi Dario & Meng, > >> > > >> > Thanks for your analysis! > >> > > >> > VM1 and VM2 both are given 8 vCPUs and sharing physical CPU 0-7. So in > >> > theory,"VM1 can get the services of 400%" > >> > And yes, Dario, your explanation about the task utilization is > correct. > >> > > >> > So the resource configuration as I mentioned before is: > >> > > >> > 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 10000 and budget of 5000) > >> > 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. > >> > > >> > Attached is the result plot. > >> > > >> > > >> > I have tried with the newest litmust-rt, and rtxen is still performing > >> > poorly. > >> > >> What is the characteristics of tasks you generated? When a taskset > >> miss ddl., which task inside miss deadline? > >> > >> Meng > >> > >> > >> > > >> > Thank you both very much again, if there is any unclear part, please > >> > lemme > >> > know, thx! > >> > > >> > Victor > >> > > >> > > >> > > >> > On Fri, Nov 27, 2015 at 9:41 AM, Meng Xu <xumengpa...@gmail.com> > wrote: > >> >> > >> >> 2015-11-27 12:23 GMT-05:00 Dario Faggioli <dario.faggi...@citrix.com > >: > >> >> > On Fri, 2015-11-27 at 08:36 -0800, Yu-An(Victor) Chen wrote: > >> >> >> Hi Dario, > >> >> >> > >> >> > Hi, > >> >> > > >> >> >> Thanks for the reply! > >> >> >> > >> >> > You're welcome. :-) > >> >> > > >> >> > I'm adding Meng to Cc... > >> >> > > >> >> > >> >> Thanks! :-) > >> >> > >> >> >> My goal for the experiment is to show that xen rtds scheduler is > >> >> >> better than credit scheduler when it comes to real time tasks. > >> >> >> so my set up is: > >> >> >> > >> >> >> for xen-credit : 2vms sharing 8 cores (cpu 0-7) using credit > >> >> >> scheduler(both with weight of 800 and capacity of 400) > >> >> > >> >> So you set up 400% cpu cap for each VM. In other words, each VM will > >> >> have computation capacity almost equal to 4 cores. Because VCPUs are > >> >> also scheduled, the four-core capacity is not equal to 4 physical > core > >> >> in bare metal, because the resource supplied to tasks from VCPUs also > >> >> depend on the scheduling pattern (which affect the resource supply > >> >> pattern) of the VCPUs. > >> >> > >> >> >> for xen-rtds: 2 vms sharing 8 cores (cpu0-7) using RTDS (both with > >> >> >> period of 10000 and budget of 5000) > >> >> > >> >> How many VCPUs for each VM? If each VM has 4 VCPU, each VM has only > >> >> 200% CPU capacity, which is only half compared to the configuration > >> >> you made for credit scheduler. > >> >> > >> >> >> in both setup, dom0 is using 1 core from cpu 8-15 > >> >> > >> >> Do you have some quick evaluation report (similar to the evaluation > >> >> section in academic papers) that describe how you did the > experiments, > >> >> so that we can have a better guess on where goes wrong. > >> >> > >> >> Right now, I'm guessing that: the resource configured for each VM > >> >> under credit and rtds schedulers are not the same, and it is possible > >> >> that some parameters are not configured correctly. > >> >> > >> >> Another thing is that: > >> >> credit scheduler is work conserving, while RTDS is not. > >> >> So under the under-loaded situation, you will see credit scheduler > may > >> >> work better because it try to use as much resource as it could. You > >> >> can make the comparision more failrly by setting the cap for credit > >> >> scheduler as you did, and running some background VM or tasks to > >> >> consume the idle resource. > >> >> > >> >> Meng > >> > > >> > > >> > >> > >> > >> -- > >> > >> > >> ----------- > >> Meng Xu > >> PhD Student in Computer and Information Science > >> University of Pennsylvania > >> http://www.cis.upenn.edu/~mengxu/ > > > > > > > > -- > > > ----------- > Meng Xu > PhD Student in Computer and Information Science > University of Pennsylvania > http://www.cis.upenn.edu/~mengxu/ >
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