Of course you don't have a CPU bottleneck with curl, it does not run 3 or 4 hashes over everything it downloads. APT needs to hash its downloads to ensure they are secure, and it uses all available hashes to do so, so if one hash's security is compromised, we can still hopefully still rely on the others.
And the topic of this bug report is indeed hash CPU usage, and I compared our CPU usage on a 1 GB test file in a tmpfs to the CPU usage of OpenSSL and Nettle. So this test operates on a data size 5 times higher than the usual packages and under optimal conditions to evaluate how fast we can hash. The test shows that on a 1 Gbit/s connection you'll likely be throttled slightly at a comparable CPU (assuming the connection reaches about 800 Mbit/s, that is, 80% efficiency). If you have a data rate of about 500 Mbit/s, you will likely be fine (not counting parallel downloads). If there are other problems reducing the download speeds, these are separate bugs. This one covers the overhead of hashing, nothing else. BTW: The original bug report talks about 20% CPU usage on a 5 year old CPU, that seems entirely reasonable and not really an issue. If your bandwidth is high, you'll have higher CPU usage for a shorter time (like 100% for 5 seconds or so). -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to apt in Ubuntu. https://bugs.launchpad.net/bugs/1123272 Title: high cpu usage on download (not optimised SHA256, SHA512, SHA1) Status in apt package in Ubuntu: Confirmed Bug description: http process takes about 20% on intel i5-3317. Here is output of ps aux: root 4309 21.7 0.0 37108 2344 pts/2 S+ 18:17 0:01 /usr/lib/apt/methods/http it can be easy reproduces with "apt-get download firefox-dbg" or any other upgrade realted command. The reason of this overhead are this functions: 22,34% http libapt-pkg.so.4.12.0 [.] SHA256_Transform(_SHA256_CTX*, unsigned int const*) 14,81% http libapt-pkg.so.4.12.0 [.] SHA512_Transform(_SHA512_CTX*, unsigned long const*) 8,11% http libapt-pkg.so.4.12.0 [.] SHA1Transform(unsigned int*, unsigned char const*) 5,62% http libapt-pkg.so.4.12.0 [.] MD5Transform(unsigned int*, unsigned int const*) libapt uses own implementation of this hasches without any optimisation. Are there any reason why libapt do not use openssl? Beside current version of openssl has AVX optimised SHA* implementations. ProblemType: Bug DistroRelease: Ubuntu 13.04 Package: apt 0.9.7.7ubuntu1 ProcVersionSignature: Ubuntu 3.8.0-4.9-generic 3.8.0-rc6 Uname: Linux 3.8.0-4-generic x86_64 ApportVersion: 2.8-0ubuntu4 Architecture: amd64 Date: Tue Feb 12 18:12:33 2013 InstallationDate: Installed on 2012-09-13 (152 days ago) InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Alpha amd64 (20120913.1) MarkForUpload: True ProcEnviron: TERM=xterm PATH=(custom, no user) XDG_RUNTIME_DIR=<set> LANG=de_DE.UTF-8 SHELL=/bin/bash SourcePackage: apt UpgradeStatus: Upgraded to raring on 2013-02-06 (5 days ago) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/apt/+bug/1123272/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
