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[71.184.142.128]) by smtp.gmail.com with ESMTPSA id bs25-20020ac86f19000000b0035d432f5ba3sm5521963qtb.17.2023.01.19.12.57.17 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Jan 2023 12:57:17 -0800 (PST) From: Eric Chanudet To: Alexander Viro Cc: linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Alexander Larsson , Andrew Halaney , Eric Chanudet Subject: [RFC PATCH 0/1] fs/namespace: defer free_mount from namespace_unlock Date: Thu, 19 Jan 2023 15:55:20 -0500 Message-Id: <20230119205521.497401-1-echanude@redhat.com> X-Mailer: git-send-email 2.39.0 MIME-Version: 1.0 Content-type: text/plain Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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