2015-05-25 21:25 GMT+02:00 Sebastian Boehm <sebast...@sometimesfood.org>: > Hi, > > On 25 May 2015 at 16:58, Julian Andres Klode <j...@debian.org> wrote: >> Those seem to be uncached or on compressed indices, and thus not >> relevant for this bug. > > fair enough. Still, even with cached and uncompressed indices a single > apt-cache show takes about 1.6 seconds on jessie and about 1.2 seconds > on wheezy.
My slowest machine has 0.9 seconds on the first run, and 0.09 on all subsequent ones, once the indices have been read into the kernel's cache. > >>> How about using the O_CLOEXEC flag when opening files? >> >> We do, AFAIK. > > Wouldn't that render the fcntl calls superfluous? Also I can't find > any relevant occurences of O_CLOEXEC in the codebase (apart from one > in pkgDPkgPM::StartPtyMagic). Right, sorry, we do not really use O_CLOEXEC, we use FD_CLOEXEC on descriptors we open, by calling SetCloseExec(). Anyway, apart from the race with that, there might be some open fds we have inherited and code using libapt-pkg might open other fds, so it's a good idea to set FD_CLOEXEC anyway. > >> 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). > > Interesting. You haven't set your Apt::ARCHITECTURES to a single arch > by any chance, have you? No, it's multi-arch. > >> 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. > > While this version is still a bit slower than the one in wheezy, it is > significantly faster than the one currently in jessie: > > Most recent git version: > ~ # time apt-cache show mg > /dev/null > apt-cache policy mg > /dev/null 0.01s user 0.00s system 51% cpu 0.015 total > > apt 1.0.9.8 (jessie): > ~ # time apt-cache show mg > /dev/null > apt-cache show mg > /dev/null 0.01s user 0.04s system 92% cpu 0.061 total > > On the docker instance on my laptop with uncompressed indices I'm down > from 2.2s to 1.4s. All in all a noticeable improvement. It might have been significantly faster in the previous commit because the sysconf() was moved out of the loop (released in 1.0.9.10), but using /proc/self/fd sped it up even further. -- Julian Andres Klode - Debian Developer, Ubuntu Member See http://wiki.debian.org/JulianAndresKlode and http://jak-linux.org/. -- To UNSUBSCRIBE, email to debian-bugs-dist-requ...@lists.debian.org with a subject of "unsubscribe". Trouble? Contact listmas...@lists.debian.org
