Hallo Gabriel F. T. Gomes, 25.11.18 15:35 Gabriel F. T. Gomes: > On 25 Nov 2018, Timo Weingärtner wrote: > >with the last upgrade of bash-completion completing hostnames has > >become slow (takes more than two seconds). My /etc/ssh/ssh_known_hosts > >file has quite some size (23084 lines / 12 MB), but this was not a > >problem with the previous implementation. > > OK, sounds like a lot of time. > > >I guess the problem is the while read … done < known_hosts_file loop, > >where the shell has to read() one byte at a time, causing a massive > >amount of syscalls (which have become even more costly this year).
OK, it is not the one-byte-per-read()-problem, which still occurs with pipes; bash has an optimisation for seek()able files and read()s 128 bytes per call, then seek()s back to behind the line terminator. > I have backported a patch [1] from the upstream master branch, in order > to fix bug #848125 [2]. Running the following command against current > upstream sources shows that there are no newer patches related to this > (lines 1479 to 1665 contain the function, _known_hosts_real, that > parses the known_hosts file): > > git log --stat -L1479,1665:bash_completion > (lastest commit is the patch that I backported [1]) Before reporting the bug I read the changelog and a quick research found that code change as a debian patch. > I think we need to forward this problem report upstream. Do you have > more information that I could add to it (maybe the syscall trace you > ran)? $ time bash -c 'while read -ra line; do :; done' < kh_file real 0m0,811s user 0m0,749s sys 0m0,059s I can't provide my /etc/ssh/ssh_known_hosts file because it contains information some people consider confidential. But I can say that for a host in that file there are several names (up to 221) and multiple key( type)s aka duplicate hostlists (up to 3). > PS: I don't want to remove the patch from Debian, because it would only > solve the problem you are reporting until bash-completion 2.9 is > released. Of course. I'll try to hack something with the same features using only essential tools (cut, grep, tr, sed, …) that will do in under 0,1s with the same input. Grüße Timo
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