Control: tag -1 pending 2015-05-25 16:22 GMT+02:00 Sebastian Boehm <[email protected]>: > Hi, > > On 25 May 2015 at 15:32, Julian Andres Klode <[email protected]> wrote: >> I don't really see the performance issue here, though. I don't know >> why the submitter thinks that there is a performance issue here. The >> closing takes a few milliseconds. An apt-cache show runs in 0.040s >> here, and has never taken longer for me. > > on my fastest machine, a single apt-cache show takes 0.06s on Jessie. > However, the same apt-cache show takes less than 0.006s on Wheezy. > > For a single run on a fast machine, this isn't too bad, but on a slow > machine this really hurts a lot. When running docker on my laptop, a > single apt-cache show takes about 2.7 seconds on jessie, whereas it > took only 1.4 seconds on wheezy. > > Jessie: > > root@b49835d0cc64:~# time apt-cache show mg > /dev/null > real 0m2.708s > user 0m1.830s > sys 0m0.850s > > Wheezy: > > root@df40952198bb:~# time apt-cache show mg > /dev/null > real 0m1.441s > user 0m1.260s > sys 0m0.190s
Those seem to be uncached or on compressed indices, and thus not relevant for this bug. > > Even the 0.06s are quite noticeable when using tools such as Chef, > which produce one apt-cache call per package check. On my fastest > machine, checking the status for ~70 packages used to take > approximately 400ms on wheezy, but takes more than four seconds with > jessie. Obviously the situation is much worse with docker and on > slower systems. > >> So I'd prefer to just close this, as it's not worth the extra effort >> to read out /proc/self/fd. > > How about using the O_CLOEXEC flag when opening files? We do, AFAIK. I'm wondering a bit because show only does about 38 fcntl() calls for me, it does not seem to ForkExec() here at all (and I don't know why it should do that at all). I just tested the closing call, and it took about 4 ms (or 10-12 in jessie) for the program to start up, call fcntl() on the 65533 file descriptors, and exit. I cannot believe that this is the major performance difference you are experiencing between wheezy and jessie. Anyway, I fixed this in http://anonscm.debian.org/cgit/apt/apt.git/commit/?id=870a2b6d683e58c0584bbd3614a76cf25a055928 to use /proc/self/fd where available. This brings us down to 0.72 ms in my optimal test case. -- Julian Andres Klode - Debian Developer, Ubuntu Member See http://wiki.debian.org/JulianAndresKlode and http://jak-linux.org/. -- To UNSUBSCRIBE, email to [email protected] with a subject of "unsubscribe". Trouble? Contact [email protected]
