[Bug 256375] iflib/if_em: unplugging network cable causes huge KTorrent slowdown

From: <bugzilla-noreply_at_freebsd.org>
Date: Thu, 03 Jun 2021 04:25:37 +0000
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=256375

--- Comment #3 from Alexey Dokuchaev <danfe_at_FreeBSD.org> ---
Created attachment 225516
  --> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=225516&action=edit
dtrace output, cable unplugged

Alexander suggested I run the following DTrace script, with and without the
cable, to see if the problem has something to do with the lock or rather
em_if_update_admin_status():

dtrace -n 'fbt::iflib_media_status:entry { self->ts = timestamp; }
fbt::iflib_media_status:return /self->ts/ {_at_[execname, "ns"] =
quantize(timestamp - self->ts); self->ts = 0; }'

So, two things: 1) KTorrent is not required to reproduce the bug (good),
ifconfig(8) is also slowed down, these is actually a visible delay of its
console output when I run without the cable; and 2) apparently
em_if_update_admin_status() is bogusly and repeatedly checking hw link status
despite, as Alexander had mentioned, that there actually is a link status field
which is being checked in other functions.

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Received on Thu Jun 03 2021 - 04:25:37 UTC

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