Spot on, grischka! Initial experiments indicate that changing the offset alignment from 16 to 512 bytes (i.e. 15 to 511) solves this problem. I'll try a few more experiments to be sure, though. I suspect that this number should be tuned to the underlying architecture, but that's not central to the discussion.
David On Thu, Jan 5, 2017 at 6:46 PM, grischka <[email protected]> wrote: > You might try larger "section alignment" for -run: > > in tccrun.c:208 instead of > offset = (offset + 15) & ~15; > for example > offset = (offset + 63) & ~63; > > This would add more space between your "foo" data variable and > the instructions in memory > > --- grischka > > > Harry van Haaren wrote: > >> On Thu, Jan 5, 2017 at 2:12 PM, avih <[email protected]> wrote: >> >>> I can reproduce x30 variations on Windows with tcc64 (built either using >>> >> gcc (mingw) or using tcc64 itself), but for me -DNOPS=2 or 5 or 9 are >> fast, >> and the others (up to 9) are slow. I didn't check further. >> >>> I also removed the #include <stdio.h> since it's not where tcc typically >>> >> is, and it's not required as far as I can tell, and also removed the -B >> thingy (the tcc binary is in the distribution dir on windows and its >> default -B location doesn't include anything other than tcc >> files/libs/includes). >> >> Same here, removed the stdio include and -B. flag, tcc version 0.9.26 >> (x86-64 Linux), recent desktop CPU: >> Results (below), even NOPS are bad, odd NOPS are good up to 8, then it >> becomes unpredictable. >> >> Hope that helps, -Harry >> >> PS: My first post to TCC list - awesome project - thanks all! :) >> >> >> time tcc -DNOPS=0 -run test.c >> real 0m1.015s >> >> time tcc -DNOPS=1 -run test.c >> real 0m0.043s >> >> time tcc -DNOPS=2 -run test.c >> real 0m1.215s >> >> time tcc -DNOPS=3 -run test.c >> real 0m0.037s >> >> time tcc -DNOPS=4 -run test.c >> real 0m1.008s >> >> time tcc -DNOPS=5 -run test.c >> real 0m0.051s >> >> time tcc -DNOPS=6 -run test.c >> real 0m1.010s >> >> time tcc -DNOPS=7 -run test.c >> real 0m0.036s >> >> time tcc -DNOPS=8 -run test.c >> real 0m1.014s >> >> time tcc -DNOPS=9 -run test.c >> real 0m1.112s >> >> time tcc -DNOPS=10 -run test.c >> real 0m0.041s >> >> time tcc -DNOPS=11 -run test.c >> real 0m1.161s >> >> time tcc -DNOPS=12 -run test.c >> real 0m0.039s >> >> time tcc -DNOPS=13 -run test.c >> real 0m1.482s >> >> time tcc -DNOPS=14 -run test.c >> real 0m1.009s >> >> time tcc -DNOPS=15 -run test.c >> real 0m1.506s >> >> time tcc -DNOPS=16 -run test.c >> real 0m1.005s >> >> >> >> >>> On Thursday, January 5, 2017 3:25 PM, David Mertens < >>> >> [email protected]> wrote: >> >>> >>> Hello everyone, >>> >>> I have now written a very simple C program which gives highly erratic >>> >> timing behavior when run under tcc -run. I have added this file to the >> gist; look for cache-test-simple.c here: https://gist.github.com/ >> run4flat/ >> fcbb6480275b1b9dcaa7a8d3a80846 38 >> >>> The simple program does not attempt to produce a shared object library, >>> >> and so should be runnable on any operating system that supports tcc -run, >> including Windows and Mac in addition to Linux. Here are some sample >> outputs on my machine: >> >>> $ time ./tcc -B. -DNOPS=0 -run cache-test-simple.c >>> real 0m0.052s >>> $ time ./tcc -B. -DNOPS=1 -run cache-test-simple.c *** >>> real 0m1.413s >>> $ time ./tcc -B. -DNOPS=2 -run cache-test-simple.c >>> real 0m0.069s >>> $ time ./tcc -B. -DNOPS=3 -run cache-test-simple.c >>> real 0m0.076s >>> $ time ./tcc -B. -DNOPS=4 -run cache-test-simple.c *** >>> real 0m1.158s >>> >>> The starred results are over an order of magnitude slower than the >>> >> unstarred results. >> >>> 1) Do others see this on other operating systems with 64-bit Intel >>> >> processors? >> >>> 2) Do others see this on any operating system with 64-bit AMD processors? >>> 3) Do others see this on any operating system with any other >>> architecture? >>> >>> Thanks! >>> David >>> >>> On Thu, Jan 5, 2017 at 12:59 AM, David Mertens <[email protected] >>> > >>> >> wrote: >> >>> Update: I *can* get this slowdown with tcc. The main trigger is to have a >>> >> global variable that gets modified by the function. >> >>> I have updated the gist: https://gist.github.com/ run4flat/ >>> >> fcbb6480275b1b9dcaa7a8d3a80846 38 >> >>> This program generates a single function filled with a collection of >>> >> skipped operations (number of operations is a command-line option) and >> finished with a modification of a global variable. It compiles the >> function >> using tcc, then calls the function a specified number of times (repeat >> count specified via command-line). It can either generate code in-memory, >> or it can generate a .so file and load that using dlopen. (If it generates >> in-memory, it prints the size of the generated code.) >> >>> Here are the interesting results on my machine, all for 10,000,000 >>> >> iterations, using compilation-in-memory: >> >>> N Code Size (Bytes) Time (s) >>> 0 128 2.52 >>> 1 144 2.54 >>> 2 176 2.57 >>> 3 208 0.035 >>> 4 224 0.058 >>> 5 256 2.57 >>> 6 272 0.060 >>> >>> Switching over to a shared object file, I get these results (code size is >>> >> size of the .so file): >> >>> N Code Size (Bytes) Time (s) >>> 0 2960 0.057 >>> 1 2984 0.040 >>> 2 3016 0.058 >>> 3 3040 0.039 >>> 4 3064 0.040 >>> 5 3088 0.060 >>> 6 3112 0.063 >>> >>> As you can see, the jit-compiled code has odd jumps of 30x speed drops >>> >> depending on... something. The shared object file, on the other hand, has >> consistently sound performance. >> >>> Two questions: >>> 1) Can anybody reproduce these effects on their Linux machines, >>> >> especially different architectures? (I can try an ARM tomorrow.) >> >>> 2) Is there something special about how tcc builds a shared object file >>> >> that is not happening with the jit-compiled code? >> >>> Thanks! >>> David >>> >>> -- >>> "Debugging is twice as hard as writing the code in the first place. >>> Therefore, if you write the code as cleverly as possible, you are, >>> by definition, not smart enough to debug it." -- Brian Kernighan >>> >>> >>> >>> >>> -- >>> "Debugging is twice as hard as writing the code in the first place. >>> Therefore, if you write the code as cleverly as possible, you are, >>> by definition, not smart enough to debug it." -- Brian Kernighan >>> >>> _______________________________________________ >>> Tinycc-devel mailing list >>> [email protected] >>> https://lists.nongnu.org/mailman/listinfo/tinycc-devel >>> >>> >>> >>> _______________________________________________ >>> Tinycc-devel mailing list >>> [email protected] >>> https://lists.nongnu.org/mailman/listinfo/tinycc-devel >>> >>> >> >> ------------------------------------------------------------------------ >> >> _______________________________________________ >> Tinycc-devel mailing list >> [email protected] >> https://lists.nongnu.org/mailman/listinfo/tinycc-devel >> > > > > _______________________________________________ > Tinycc-devel mailing list > [email protected] > https://lists.nongnu.org/mailman/listinfo/tinycc-devel > -- "Debugging is twice as hard as writing the code in the first place. Therefore, if you write the code as cleverly as possible, you are, by definition, not smart enough to debug it." -- Brian Kernighan
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