Bug#409872: On slow arch apt just wastes cpu while waiting for dpkg to run
Package: apt
Version: 0.6.46.4
Severity: normal
I'm running apt from an nfs-mounted chroot of the real disk inside a
qemu-system-arm instance. This is quite slow, but better than the real machine
(nslu2) which has infeasibly little memory (32MB) [When I was young...],
at least for modern big package databases.
However, I notice that while dpkg is running to decompress something,
apt is still taking about as much cpu as the dpkg instance. This is sad,
giving that all its doing is waiting.
strace reveals:
....
read(4, 0xbea58906, 1) = -1 EAGAIN (Resource temporarily unavailable)
nanosleep({0, 1000000}, NULL) = 0
wait4(12980, 0xbea58758, WNOHANG, NULL) = 0
read(4, 0xbea58906, 1) = -1 EAGAIN (Resource temporarily unavailable)
nanosleep({0, 1000000}, NULL) = 0
....
So its got a wait4 and a 1ms delay. A real ARM chip is a disaster on context
switches (need to flush the cache - it uses virtual addresses.) I guess
qemu-ed it is as well.
So I guess I'm asking for this particular bit of code to be fixed to be a bit
more gentle. There shouldn't be much slowdown on faster arches, and it
could double the speed in this case. Maybe it could do a smart backoff
or something. Or indeed just 10ms instead of 1ms would be enough.
-- Package-specific info:
-- apt-config dump --
APT "";
APT::Architecture "arm";
APT::Build-Essential "";
APT::Build-Essential:: "build-essential";
APT::Authentication "";
APT::Authentication::TrustCDROM "true";
Dir "/";
Dir::State "var/lib/apt/";
Dir::State::lists "lists/";
Dir::State::cdroms "cdroms.list";
Dir::State::userstatus "status.user";
Dir::State::status "/var/lib/dpkg/status";
Dir::Cache "var/cache/apt/";
Dir::Cache::archives "archives/";
Dir::Cache::srcpkgcache "srcpkgcache.bin";
Dir::Cache::pkgcache "pkgcache.bin";
Dir::Etc "etc/apt/";
Dir::Etc::sourcelist "sources.list";
Dir::Etc::sourceparts "sources.list.d";
Dir::Etc::vendorlist "vendors.list";
Dir::Etc::vendorparts "vendors.list.d";
Dir::Etc::main "apt.conf";
Dir::Etc::parts "apt.conf.d";
Dir::Etc::preferences "preferences";
Dir::Bin "";
Dir::Bin::methods "/usr/lib/apt/methods";
Dir::Bin::dpkg "/usr/bin/dpkg";
DPkg "";
DPkg::Pre-Install-Pkgs "";
DPkg::Pre-Install-Pkgs:: "/usr/bin/apt-listchanges --apt || test $? -ne 10";
DPkg::Pre-Install-Pkgs:: "/usr/sbin/dpkg-preconfigure --apt || true";
DPkg::Tools "";
DPkg::Tools::Options "";
DPkg::Tools::Options::/usr/bin/apt-listchanges "";
DPkg::Tools::Options::/usr/bin/apt-listchanges::Version "2";
-- (no /etc/apt/preferences present) --
-- /etc/apt/sources.list --
deb http://ftp.uk.debian.org/debian/ etch main
#deb http://debian.hands.com/debian/ sid main
#deb-src http://ftp.uk.debian.org/debian/ etch main
deb http://security.debian.org/ etch/updates main
#deb-src http://security.debian.org/ etch/updates main
-- System Information:
Debian Release: 4.0
APT prefers testing
APT policy: (500, 'testing')
Architecture: arm (armv5tel)
Shell: /bin/sh linked to /bin/bash
Kernel: Linux 2.6.18-3-ixp4xx
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968)
Versions of packages apt depends on:
ii debian-archive-keyring 2006.11.22 GnuPG archive keys of the Debian a
ii libc6 2.3.6.ds1-10 GNU C Library: Shared libraries
ii libgcc1 1:4.1.1-21 GCC support library
ii libstdc++6 4.1.1-21 The GNU Standard C++ Library v3
apt recommends no packages.
-- no debconf information
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