On Wed, Jan 03, 2001 at 07:37:22PM -0500, Guido van Rossum wrote:
> > In other words: use it! :)
>
> Mind doing a few platform tests on the (new version of the) patch?
Well, only a bit :) It's annoying that BSDI doesn't come with autoconf, but
I managed to use all my early-morning wit (it's 6:30AM <wink>) to work
around it. I've tested it on BSDI 4.1 and FreeBSD 4.2-RELEASE.
> I already know that it works on Red Hat Linux 6.2 (my box) and Solaris
> 2.6 (Andrew's box). I would be delighted to know that it works on at
> least one other platform that has getc_unlocked() and one platform
> that doesn't have it!
Sorry, I have to disappoint you. FreeBSD does have getc_unlocked, they
just didn't document it. Hurrah for autoconf ;P Anyway, it worked like a
charm on BSDI:
(Python 2.0)
total 1794310 chars and 37660 lines
count_chars_lines 0.310 0.300
readlines_sizehint 0.150 0.150
using_fileinput 2.013 2.017
while_readline 1.006 1.000
(CVS Python + getc_unlocked)
daemon2:~/python/python/dist/src > ./python test.py termcapx10
total 1794310 chars and 37660 lines
count_chars_lines 0.354 0.350
readlines_sizehint 0.182 0.183
using_fileinput 1.594 1.583
while_readline 0.363 0.367
But something weird is going on on FreeBSD:
(Standard CVS Python)
> ./python ~thomas/test.py ~thomas/termcapx10
total 1794310 chars and 37660 lines
count_chars_lines 0.265 0.266
readlines_sizehint 0.148 0.148
using_fileinput 0.943 0.938
while_readline 0.214 0.219
(CVS+getc_unlocked)
> ./python-getc-unlocked ~thomas/test.py ~thomas/termcapx10
total 1794310 chars and 37660 lines
count_chars_lines 0.266 0.266
readlines_sizehint 0.151 0.141
using_fileinput 1.066 1.078
while_readline 0.283 0.281
This was sufficiently unexpected that I looked a bit further. The FreeBSD
Python was compiled without editing Modules/Setup, so it was statically
linked, no readline etc, but *with* threads (which are on by default, and
functional on both FreeBSD and BSDI 4.1.) Here's the timings after I enabled
just '*shared*':
(CVS + *shared*)
> ./python ~thomas/test.py ~thomas/termcapx10
total 1794310 chars and 37660 lines
count_chars_lines 0.276 0.273
readlines_sizehint 0.150 0.156
using_fileinput 0.902 0.898
while_readline 0.206 0.203
(This was not a fluke, I repeated it several times, getting hardly any
variation.) Enabling readline and cursesmodule had no additional effect.
Adding *shared* to the getc_unlocked tree saw roughly the same improvement,
but was still slower than without getc_unlocked.
(CVS + *shared* + getc_unlocked)
> ./python ~thomas/test.py ~thomas/termcapx10
total 1794310 chars and 37660 lines
count_chars_lines 0.272 0.273
readlines_sizehint 0.149 0.148
using_fileinput 1.031 1.031
while_readline 0.267 0.266
Increasing the size of the testfile didn't change anything, other than the
absolute numbers. I browsed stdio.h, where both getc() and getc_unlocked()
are defined as macros. getc_unlocked is defined as:
#define __sgetc(p) (--(p)->_r < 0 ? __srget(p) : (int)(*(p)->_p++))
#define getc_unlocked(fp) __sgetc(fp)
and getc either as
#define getc(fp) getc_unlocked(fp)
(without threads) or
static __inline int \
__getc_locked(FILE *_fp) \
{ \
extern int __isthreaded; \
int _ret; \
if (__isthreaded) \
_FLOCKFILE(_fp); \
_ret = getc_unlocked(_fp); \
if (__isthreaded) \
funlockfile(_fp); \
return (_ret); \
}
#define getc(fp) __getc_locked(fp)
_FLOCKFILE(x) is defined as flockfile(x), so that isn't the difference. The
speed difference has to be in the quick-and-easy test for whether the
locking is even necessary. Starting a thread on 'time.sleep(900)' in test.py
shows these numbers:
(standard CVS python)
> ./python-shared-std ~/test.py ~/termcapx10
total 1794310 chars and 37660 lines
count_chars_lines 0.433 0.445
readlines_sizehint 0.204 0.188
using_fileinput 1.595 1.594
while_readline 0.456 0.453
(getc_unlocked)
> ./python-getc-unlocked-shared ~/test.py ~/termcapx10
total 1794310 chars and 37660 lines
count_chars_lines 0.441 0.453
readlines_sizehint 0.206 0.195
using_fileinput 1.677 1.688
while_readline 0.509 0.508
So... using getc_unlocked manually for performance reasons isn't a cardinal
sin on FreeBSD only if you are really using threads :-)
Lets-outsmart-the-OS-scheduler-next!-ly y'rs
--
Thomas Wouters <thomas@xs4all.net>
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