Control: retitle -1 dpkg: package install can be very slow with some disks due to too frequent fsync
Hi, On 2019-04-09 00:33:27 +0200, Guillem Jover wrote: > On Tue, 2019-03-05 at 15:43:05 +0100, Vincent Lefevre wrote: > > zira:~> iozone -a -e > > [...] > > random > > random bkwd record stride > > kB reclen write rewrite read reread read > > write read rewrite read fwrite frewrite fread freread > > 64 4 1821 1987 1922 3703 3657 > > 1770 1621 1628 1697 1707 1773 1879725 2892445 > > 64 8 1606 1684 1713 3493 3476 > > 1700 1765 1730 1812 2135 1852 2278628 3406295 > > 64 16 1807 1823 1986 3898 3798 > > 1977 1813 1988 1871 2049 3320 2561267 4018152 > > 64 32 1702 1714 1755 3494 3683 > > 1741 1841 1796 1737 1633 1674 1879725 4018152 > > 64 64 1808 1790 1632 3314 3387 > > 2254 1995 1843 1984 1789 1820 2801873 3203069 > > [...] > > Ok, can we conclude this is not a problem in dpkg then? :) I'm not sure. This may just be a slow disk after all, and in practice (I mean except benchmarking), the problem seems specific to dpkg. I assume that programs normally don't do a fsync at every fraction of microsecond! I don't know what dpkg is trying to achieve with such a frequency of fsync, but this doesn't seem to make sense to me. You had said "which has been the solution to earlier problems with ext4", but the real solution would be to fix ext4 (does "earlier" mean this has eventually been fixed?). > It seems to me either hardware, filesystem or kernel related as > mentioned before. I've seen https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1785020 "fsync is slow on later kernels with ext4 filesystms" but the comments in this bug page and 4.19.28-1 kernel logs show that this has been fixed. FYI, I get very similar timings on the same machine, but on /boot, which is: /dev/sda1 on /boot type ext2 (rw,relatime,block_validity,barrier,user_xattr,acl,stripe=4) The fact that the main, ext4 partition is encrypted but not this one makes another difference, but the timings are similar, so that this doesn't seem to be related to the FS system itself and appears to be at a lower level. Note also that my machine is a laptop, and I couldn't do a comparison with other laptops, just in case. > Could you reassign where you think it would be more appropriate? I think that this should still be regarded as a dpkg bug, based on my first paragraph above (the fsync's occur much too often in dpkg compared to other programs, and this doesn't seem to be useful). -- Vincent Lefèvre <[email protected]> - Web: <https://www.vinc17.net/> 100% accessible validated (X)HTML - Blog: <https://www.vinc17.net/blog/> Work: CR INRIA - computer arithmetic / AriC project (LIP, ENS-Lyon)
