On Tue, Mar 3, 2015 at 6:44 PM, Anthony Ferrara <ircmax...@gmail.com> wrote:
> Zeev, > > On Tue, Mar 3, 2015 at 8:05 AM, Zeev Suraski <z...@zend.com> wrote: > >> So I do apologize to the person. I don't to the code. > > > > I wanted to verify whether my gut was correct (minimal amount of output, > and > > stdout is in fact buffered - output shouldn't move the needle) and asked > > Dmitry to rerun the C test on the same system, but this time with the > output > > code completely commented out: > > real 0m0.011s (+- 0.01) > > user 0m0.011s (+- 0.01) > > sys 0m0.001s > > > > Apologies to the code might be in order :) > > > > The source of the JIT engine's edge is, as Dmitry and Andi said, the > > CPU-specific optimizations that gcc -O2 doesn't generate, and therefore > it > > can actually be faster than a generic native executable in some (I would > > guess not all that common) cases. > > So, let's put that to the test, shall we. I compiled and ran the "JIT" > compiler (can we please stop calling it that, it's not). This is JIT! > along side > PHP 5.5, PHP 7 and GCC -O0 through -O3. > > I also turned on the ob_start and off (commenting out the ob_start and > ob_end_flush lines): > ope > > https://docs.google.com/spreadsheets/d/1b4yFh0i62haDoQBRf8pOoi63OLrxRbecHSj9sQpD5Nk/edit?usp=sharing > > With ob_start, the "JIT" was fastest. Without it, it was more than 2x > slower (slightly faster than -O0). > C FILE API is buffering as well. I hope you knew. Use write() instead of printf() in C to disable buffering as well. Raw results (average): > > GCC -O0: 0.0258 > GCC -O1: 0.0160 > GCC -O2: 0.0144 > GCC -O3: 0.0140 > "JIT" /w ob_start: 0.011 > "JIT" /wo ob_start: 0.0238 > 5.5 /w: 1.273 > 5.5 /wo: 1.301 > 7 /w: 1.492 > 7 /wo: 1.545 > > I used identical code to what Dmitry posted earlier, with the one > exception that ob_start was commented out for the "/wo" runs. > Now, there's something really interesting in those results. The > numbers given back from the "JIT" are far more stable than anything > else (more than an order of magnitude more stable /wo, and several > orders /w ob_start). Something smells off about it. I'm not so sure > what off hand, but I'm going to dig further. > php -d opcache.jit_debug=0x100 bench.php > > Now, to the point that "gcc uses output buffering". Yes, it does. > However, PHP (including the "JIT") is compiled with GCC. So it will > use a similar output buffer unless you disable the buffer. The only > place in 7 that we do that is sapi/phpdbg/phpdbg.c:881. So either way, > you're going to be using the same output buffer on the STDOUT stream. > Please check php/sapi_cli.c and the setting of PHP_WRITE_STDOUT before claiming others. Thanks. Dmitry. > > Anthony > > -- > PHP Internals - PHP Runtime Development Mailing List > To unsubscribe, visit: http://www.php.net/unsub.php > >
