Stephane Chazelas <stephane.chaze...@gmail.com> wrote:
> 2017-05-16 17:29:13 +0100, Stephane Chazelas:
...
> szsh a 0.763
> szsh b 0.622
> ksh93 a 0.667
> ksh93 b 0.464
> yash a 0.738
> yash b 0.429
>
> In mksh, printf is not built-in which doesn't help. In all but
> ksh93, that still does 5 forks because of the $(set +o).
>
> dash is the only one that manages to be quicker (not if I use
> mawk instead of gawk though).
dash is the one of the slowest shells. It appears to be fast because it does
not support multi-byte characters, which disqualifies it for use in a normal
UNIX environment.
I made benchmarks with various shells and I know that in the Bourne Shell, 30%
of the total CPU time is spent in the multibyte -> wide -> multibyte
conversions that are needed to support stateful encodings.
As a result, it is expected to see dash slower than bash in case it was
enhanced to support multi byte chars.
Here are my results:
dash a 0,833
dash b 0,684
bash a 1,839
bash b 1,136
bosh a 1,441
bosh b 0,852
mksh a 3,601
mksh b 1,034
szsh a 1,791
szsh b 1,533
ksh a 2,970
ksh b 0,935
ksh93 a 1,303
ksh93 b 1,176
yash a 1,809
yash b 0,892
dash a 2,384
dash b 0,035
bash a 13,491
bash b 0,099
bosh a 4,400
bosh b 0,049
mksh a 20,927
mksh b 0,040
szsh a 4,771
szsh b 0,047
ksh a 13,634
ksh b 0,061
ksh93 a 1,318
./b: line 2: 21650: Terminated
ksh93 b 26,434
yash a 7,036
yash b 0,068
ksh88 is ksh...
For some reason, the awk based example does not terminate with ksh93 in your
second example. I had to kill it.
As you see, if you only look at multi-byte enabled shells, the recent POSIX
compliant Bourne Shell (bosh) and ksh93 are the fastest.
Both ksh93 and bosh avoid forks and try to use vfork instead of fork whenever
possible. Note that on a platform with a real vfork implementation (Solaris),
vfork is aprox. 3x faster than fork even though fork on Solaris is a copy on
write fork already.
Linux does not implement a real vfork, as it just gives you the disadvantages
of vfork and the shared data, while on Solaris, the vfork child borrows the
address space description from the parent.
Jörg
--
EMail:jo...@schily.net (home) Jörg Schilling D-13353 Berlin
joerg.schill...@fokus.fraunhofer.de (work) Blog: http://schily.blogspot.com/
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