Re: [rt-tests v1 4/6] cyclictest: Mimik --smp behavior with --affinity

[John Kacur <jkacur@redhat.com>]

On Tue, 26 Jan 2021, Daniel Wagner wrote:

> On Tue, Jan 26, 2021 at 12:55:33AM -0500, John Kacur wrote:
> > Well, --smp historically combined -a -t and threads at the same priority
> > You could argue that it is reasonable for -a to automatically imply -t
> > but I have had debates with people about this and we settled on -a just 
> > specifies the affinity, and the default number of threads is one unless
> > you use -t.
> 
> My thinking is if you set an affinity mask, you want also to assign a
> thread to the CPUs. If not what's the point to set an affinity mask
> without a thread on it. Though the user is able to overwrite this
> by providing the -t options along side the -a option.

Not necessarily, but you want to limit where the threads, no matter
how few or how many run. As I said, it's not an unreasonable default,
but it is not the current default of 1 unless you specify -t
I suggest we stick with the current default in this clean-up effort.
We can discuss if there are some better defaults after this effort is 
complete.

> 
> > I'm not sure what you mean by this makes cyclictest behave the way the 
> > rest of rt-tests does, the rest of rt-tests should match what cyclitest 
> > does.
> 
> As I wrote, make cyclictest behave the same way as the to other tools
> when -a/-t is used.
> 
> > That said, I did some quick runs of signaltest and -a seems broken,
> > sigh.
> 
> Is it broken without my patches or with my patches? What is broken?
> 
> 
I haven't done a git bisect or something of that sort to determine if your 
patches broke it, but here's what I see. (running on non-rt laptop now, so 
ignore numbers), but it looks like at least the -t option requiring an 
argument existed before your changes, but your changes to affinity 
probably could use some more testing.

The following is okay

./signaltest  -a1-4
2.00 1.52 1.14 2/1079 6541          

T: 0 ( 6537) P: 0 C:  14896 Min:      3 Act:    4 Avg:   26 Max:     366


The following is broken, the default without an argument should be 2
./signaltest  -t
./signaltest: option requires an argument -- 't'

In the following note that threads other than thread 0 didn't appear
on the screen until after the ctrl-c

./signaltest -t9 -a1-4
1.11 1.14 1.14 2/1075 6864          

T: 0 ( 6856) P: 0 C:   1649 Min:     38 Act:  511 Avg:  457 Max:    4911
^CT: 0 ( 6856) P: 0 C:   1660 Min:     38 Act:  554 Avg:  457 Max:    4911
T: 1 ( 6857) P: 0 C:   1660 Min:     38 Act:  490 Avg: 1090 Max:   15024
T: 2 ( 6858) P: 0 C:   1660 Min:     38 Act:  449 Avg: 1091 Max:   15053
T: 3 ( 6859) P: 0 C:   1660 Min:     38 Act:  412 Avg: 1091 Max:   15075
T: 4 ( 6860) P: 0 C:   1660 Min:     38 Act:  378 Avg: 1090 Max:   15081
T: 5 ( 6861) P: 0 C:   1659 Min:     38 Act:  517 Avg: 1091 Max:   15072
T: 6 ( 6862) P: 0 C:   1659 Min:     38 Act:  485 Avg: 1091 Max:   15067
T: 7 ( 6863) P: 0 C:   1659 Min:     38 Act:  522 Avg: 1091 Max:   12832
T: 8 ( 6864) P: 0 C:   1659 Min:     38 Act:  549 Avg: 1091 Max:   12839


etc, it's broken in many ways.