strange differencies: find -exec \+ vs find | xargs

[dennis berger]

Dear,

I suspect that you're hitting a cache limit for that machine.
I had similar behaviour when rsyncing huge directories. I usually raise vfs.ufs.dirhash_maxmem sysctl variable, which solves the problem.

best,
-dennis


Am 15.06.2011 um 12:33 schrieb Vadim Goncharov:

> Hi,
> 
> There was a flamewar in a local maillist about the fastest way to do chmod 644
> on files and chmod 755 on directories in a sbubtree. It suddenly revealed the
> strange thing: on the same subtree, find -type d -exec \+ on 76000 directories
> has the same as find | xargs, but on 246000 files it was 4 times slower - while
> there must be almost identical number of forks.
> 
> I've repeated the tests on deliberately old machine, a Pentium I 233 MHz with
> 80 Mb RAM, 7.4R UFS2. Subtree for tests was copy of /usr/src with several
> categories from /usr/ports. The output is from ZSH's builtin 'time' (also
> set up to automatically output if cmd was run more than 30 secs).
> 
> Below is the ooutput, first with 80K files, it doesn't differ, than added
> several more /usr/ports categories and got slow result on 100K. Why is
> the difference at all? This machine has maxvnodes about 4600 and too small
> RAM for caches, if that's buffers, I'd expect the difference to begin on
> mush slow number of files. But it runs the same 80K normally...
> 
> kernblitz:/home/vadim# find /warehouse/garbage -type f | wc -l; find /warehouse/garbage -type d | wc -l
>   80208
> find /warehouse/garbage -type f  5,01s user 53,12s system 53% cpu 1:48,52 total
> wc -l  0,54s user 0,31s system 0% cpu 1:48,49 total
>   13989
> find /warehouse/garbage -type d  4,52s user 52,00s system 53% cpu 1:45,63 total
> wc -l  0,11s user 0,06s system 0% cpu 1:45,61 total
> 
> kernblitz:/home/vadim# time chmod -R u+rwX,go+rX,go-w /warehouse/garbage
> chmod -R u+rwX,go+rX,go-w /warehouse/garbage  4,39s user 54,94s system 53% cpu 1:50,73 total
> 
> kernblitz:/home/vadim# time find /warehouse/garbage -type f -exec chmod 644 {} \+
> find /warehouse/garbage -type f -exec chmod 644 {} \+  7,29s user 100,30s system 65% cpu 2:43,29 total
> 
> kernblitz:/home/vadim# time find /warehouse/garbage -type d -exec chmod 755 {} \+
> find /warehouse/garbage -type d -exec chmod 755 {} \+  5,04s user 58,91s system 54% cpu 1:58,05 total
> 
> kernblitz:/home/vadim# time find /warehouse/garbage -type f -print0 | xargs -0 chmod 644
> find /warehouse/garbage -type f -print0  4,78s user 55,14s system 37% cpu 2:40,27 total
> xargs -0 chmod 644  3,26s user 46,70s system 30% cpu 2:41,26 total
> 
> kernblitz:/home/vadim# cp -r /usr/ports/[e-k]* /warehouse/garbage
> cp -r /usr/ports/[e-k]* /warehouse/garbage  4,57s user 115,70s system 29% cpu 6:54,47 total
> 
> kernblitz:/home/vadim# find /warehouse/garbage -type f | wc -l; find /warehouse/garbage -type d | wc -l
>  102014
> find /warehouse/garbage -type f  6,46s user 69,75s system 48% cpu 2:38,31 total
> wc -l  0,78s user 0,27s system 0% cpu 2:38,29 total
>   19714
> find /warehouse/garbage -type d  6,11s user 72,32s system 48% cpu 2:43,26 total
> wc -l  0,13s user 0,09s system 0% cpu 2:43,24 total
> 
> kernblitz:/home/vadim# time chmod -R u+rwX,go+rX,go-w /warehouse/garbage
> chmod -R u+rwX,go+rX,go-w /warehouse/garbage  5,59s user 69,97s system 48% cpu 2:36,53 total
> 
> kernblitz:/home/vadim# time find /warehouse/garbage -type d -exec chmod 755 {} \+
> find /warehouse/garbage -type d -exec chmod 755 {} \+  6,72s user 83,05s system 23% cpu 6:15,22 total
> 
> kernblitz:/home/vadim# time find /warehouse/garbage -type f -exec chmod 644 {} \+
> find /warehouse/garbage -type f -exec chmod 644 {} \+  10,49s user 138,30s system 20% cpu 12:14,49 total
> 
> kernblitz:/home/vadim# time find /warehouse/garbage -type f -print0 | xargs -0 chmod 644
> find /warehouse/garbage -type f -print0  6,58s user 70,84s system 35% cpu 3:36,67 total
> xargs -0 chmod 644  3,93s user 59,30s system 28% cpu 3:39,50 total
> 
> -- 
> WBR, Vadim Goncharov. ICQ#166852181       mailto:vadim_nuclight at mail.ru
> [Moderator of RU.ANTI-ECOLOGY][FreeBSD][http://antigreen.org][LJ:/nuclight]
> 
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