We noticed significant slow down when running containers on an Aarch64 system
with the RT patch set using the following test:
# mkdir -p "rootfs/bin"
# printf "int main(){return 0;}" | gcc -x c - -static -o rootfs/bin/sh
# crun spec
# perf stat -r 10 --table --null -- crun run test
Performance counter stats for 'crun run test' (10 runs):
# Table of individual measurements:
0.3902 (-0.1941) ##########
0.5791 (-0.0053) #
0.5785 (-0.0058) #
0.5891 (+0.0047) #
0.6682 (+0.0839) ###
0.5507 (-0.0337) ##
0.5888 (+0.0044) #
0.5797 (-0.0047) #
0.5977 (+0.0133) #
0.7217 (+0.1374) ####
# Final result:
0.5844 +- 0.0269 seconds time elapsed ( +- 4.60% )
A 6.2 non-RT kernel results on the same hardware for comparison:
Performance counter stats for 'crun run test' (10 runs):
# Table of individual measurements:
0.1680 (+0.1375) #################
0.0074 (-0.0231) ###############################################################
0.0073 (-0.0232) ################################################################
0.0070 (-0.0235) ####################################################################
0.0072 (-0.0233) #################################################################
0.0794 (+0.0489) #############
0.0078 (-0.0227) ##########################################################
0.0070 (-0.0235) ###################################################################
0.0070 (-0.0235) ####################################################################
0.0068 (-0.0237) ######################################################################
# Final result:
0.0305 +- 0.0169 seconds time elapsed ( +- 55.33% )
It looks like there is one bottleneck in:
-> do_umount
-> namespace_unlock
-> synchronize_rcu_expedited
With the following patch, namespace_unlock will queue up the resources that
needs to be released and defer the operation through call_rcu to return without
waiting for the grace period.
Alexander Larsson (1):
fs/namespace: defer free_mount from namespace_unlock
fs/namespace.c | 42 +++++++++++++++++++++++++++++++++++-------
1 file changed, 35 insertions(+), 7 deletions(-)
--
2.39.0
