Messages in this thread | | | From | Eric Chanudet <> | Subject | [RFC PATCH 0/1] fs/namespace: defer free_mount from namespace_unlock | Date | Thu, 19 Jan 2023 15:55:20 -0500 |
| |
We noticed a significant slow down when running a 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
| |