Re: Performance issue with systemd-coredump and container process linking 2000 shared libraries.

[Mark Wielaard <mark@klomp.org>]

Hi,

On Mon, Jun 19, 2023 at 05:08:50PM +0200, Mark Wielaard wrote:
> Just to let you know I am looking at this. But haven't made much
> progress in understanding it yet. Thanks so much for the reproducer. I
> have been able to see the (very slow) parsing of the core file with it.
> 
> $ time ./mimic-systemd-coredump
> [...]
> real	3m35.965s
> user	0m0.722s
> sys	0m0.345s
> 
> Note however that a lot of time is "missing".
> And in fact running it again is fast!?!
> 
> $ time ./mimic-systemd-coredump
> real	0m0.327s
> user	0m0.272s
> sys	0m0.050s
> 
> This is because of the kernel inode/dentry cache.
> If I do $ echo 2 | sudo tee /proc/sys/vm/drop_caches
> before running ./mimic-systemd-coredump it is always slow.
> 
> I'll try to figure out what we do to make it so hard for the kernel to
> do these lookups.

So I made a mistake here. Since I was testing on fedora 38 which has
DEBUGINFOD_URLS set. Without DEBUGINFOD_URLS set there is no big
slowdown.

Do you have the DEBUGINFOD_URLS environment variable set?

The real sd-coredump will not have DEBUGINFOD_URLS set (I hope).

Thanks,

Mark