run-this-one is very slow

Thank you for taking the time to report this bug and helping to make Ubuntu better.

I can reproduce this. I quickly instrumented run-this-one to see why it takes time. The pgrep took 5.4ms, so avoiding the pgrep won't help. The lsof call took 1376ms, so that's where most of the delay is. There's also a "sleep 0.5" in there. The sleep together with the lsof account for most of the time.

Suggestions welcome.

I'm marking Importance: Low since I can't imagine a use case where this would cause a real practical impact to Ubuntu users. If you're affected more severely, please explain your use case.

Thanks for such a quick and helpful response.

Which Ubuntu version did you try and which stack limits?

Thanks. We try!

I used a Bionic lxd container on a Hirsute host machine, with whatever the default is for limits.

There are many programming languages where some frequent programming patterns (like non tail recursion) use more stack than the default of 8192. People normally increase the stack limit in such cases, e.g.

 # ulimit -S -s 800000

The run time increase is linear in stack limit:

 # time run-this-one echo

real 3,763s user 3,012s syst 0,249s busy 86,65%
real 6,954s user 6,028s syst 0,425s busy 92,78% (with doubled stack limit)

Or even:

 # ulimit -S -s unlimited
 # time run-this-one echo
pgrep: cannot allocate 4611686018427387903 bytes

real 0,658s user 0,071s syst 0,076s busy 22,31%

OK, so we should fix pgrep to fix that. There's little sense in working around it when we can just patch pgrep in Ubuntu. You have bug 1874824 for that.

Sure, fixing the pgrep bug will be the easiest solution for run-this-one and others. Thanks for your help on bug 1878424.

Let's hope it will be in 21.04 and maybe even backported.

I meant bug 1874824.