Re: Improve hackbench

["Zhang, Yanmin" <yanmin_zhang@linux.intel.com>]

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On Fri, 2008-01-04 at 13:51 +0200, Török Edwin wrote:
> Ingo Molnar wrote:
> > * Zhang, Yanmin <yanmin_zhang@linux.intel.com> wrote:
> >
> >   
> >> hackbench is to test Linux scheduler. The original program is at 
> >> http://devresources.linux-foundation.org/craiger/hackbench/src/hackbench.c 
> >> Based on this multi-process version, a nice person created a 
> >> multi-thread version. Pls. see 
> >> http://www.bullopensource.org/posix/pi-futex/hackbench_pth.c
> >>     
> >
> > great. I've uploaded your unified & improved version to:
> >
> >   http://redhat.com/~mingo/cfs-scheduler/tools/hackbench.c
> >
> > (i made some small changes - two warning fixes on gcc 4.2 and a default 
> > of 10 groups when hackbench is called without parameters, plus a 
> > printout.)
> >   
> 
> On x86-64 there's a bug [*], that causes hackbench to segfault when
> compiled with optimizations:
> in reap_worker():
>     int status;
> ...
>     pthread_join(id, (void **)(void *)&status);
> 
> That is not correct, sizeof(void*) > sizeof(int) on x86-64.
> Something gets overwritten on the stack, I tried with gcc
> -fstack-protector, but it doesn't detect it !?
> After applying the patch, it no longer segfaults.
> 
> This patch fixes it:
Thanks.

> --- hackbench.c 2008-01-04 10:08:26.000000000 +0200
> +++ ../hackbench.c      2008-01-04 13:45:22.000000000 +0200
> @@ -241,8 +241,10 @@
>                 wait(&status);
>                 if (!WIFEXITED(status))
>                         exit(1);
> -       } else
> -               pthread_join(id, (void **)(void *)&status);
> +       } else {
> +               void* status;
> +               pthread_join(id, (void **)&status);
We could use NULL to replace &status.

> +       }
>  }
> 
>  /* One group of senders and receivers */
> 
> ----------------
> 
> 
> I also notice that the thread version is slower, than process version:
I also noticed that. I did an initial check and found the root cause might
be the difference between pthread_join and wait. wait will wait any sub-process
to exit and pthread_join just waits a specific thread to exit. If the first thread
exits lastly, it will take the main thread a longer time to reap sub-threads in the end.

> 
> $ ./hackbench 5 thread
> Running with 5*40 (== 200) tasks.
> Time: 0.413
> $ ./hackbench 5 thread
> Running with 5*40 (== 200) tasks.
> Time: 0.423
> $ ./hackbench 5 thread 20
> Running with 5*40 (== 200) tasks.
> Time: 0.093
> $ ./hackbench 5 thread 200
> Running with 5*40 (== 200) tasks.
> Time: 0.827
> $ ./hackbench 5 thread 2000
> Running with 5*40 (== 200) tasks.
> Time: 8.409
> $ ./hackbench 5 process 2000
> Running with 5*40 (== 200) tasks.
> Time: 7.669
> $ ./hackbench -pipe 5  process 2000
> Running with 5*40 (== 200) tasks.
> Time: 3.416
> $ ./hackbench -pipe 5  thread 2000
> Running with 5*40 (== 200) tasks.
> Time: 4.320
> 
> [*]
> $ uname -a
> Linux lightspeed2 2.6.24-rc6-ge697789d #3 Wed Jan 2 11:15:05 EET 2008
> x86_64 GNU/Linux
> $ gcc -v
> Using built-in specs.
> Target: x86_64-linux-gnu
> Configured with: ../src/configure -v
> --enable-languages=c,c++,fortran,objc,obj-c++,treelang --prefix=/usr
> --enable-shared --with-system-zlib --libexecdir=/usr/lib
> --without-included-gettext --enable-threads=posix --enable-nls
> --with-gxx-include-dir=/usr/include/c++/4.2 --program-suffix=-4.2
> --enable-clocale=gnu --enable-libstdcxx-debug --enable-mpfr
> --enable-checking=release --build=x86_64-linux-gnu
> --host=x86_64-linux-gnu --target=x86_64-linux-gnu
> Thread model: posix
> gcc version 4.2.3 20071123 (prerelease) (Debian 4.2.2-4)
> $ wget http://redhat.com/~mingo/cfs-scheduler/tools/hackbench.c
> --13:40:53--  http://redhat.com/~mingo/cfs-scheduler/tools/hackbench.c
>            => `hackbench.c'
> Resolving redhat.com... 209.132.177.50
> Connecting to redhat.com|209.132.177.50|:80... connected.
> HTTP request sent, awaiting response... 302 Found
> Location: http://www.redhat.com/~mingo/cfs-scheduler/tools/hackbench.c
> [following]
> --13:40:54--  http://www.redhat.com/~mingo/cfs-scheduler/tools/hackbench.c
>            => `hackbench.c'
> Resolving www.redhat.com... 209.132.177.50
> Connecting to www.redhat.com|209.132.177.50|:80... connected.
> HTTP request sent, awaiting response... 301 Moved Permanently
> Location: http://people.redhat.com/mingo/cfs-scheduler/tools/hackbench.c
> [following]
> --13:40:54--  http://people.redhat.com/mingo/cfs-scheduler/tools/hackbench.c
>            => `hackbench.c'
> Resolving people.redhat.com... 66.187.233.237
> Connecting to people.redhat.com|66.187.233.237|:80... connected.
> HTTP request sent, awaiting response... 200 OK
> Length: 8,455 (8.3K) [text/plain]
> 
> 100%[====================================================================================================================>]
> 8,455         --.--K/s
> 
> 13:40:55 (61.93 KB/s) - `hackbench.c' saved [8455/8455]
> 
> $ gcc  -O2 -g -Wall -o hackbench hackbench.c -lpthread
> hackbench.c:32:66: warning: missing terminating ' character
> $ ./hackbench 1 thread
> Running with 1*40 (== 40) tasks.
> Segmentation fault
> 
> $ valgrind --trace-children=yes ./hackbench 1 thread
> ==27332== Memcheck, a memory error detector.
> ==27332== Copyright (C) 2002-2007, and GNU GPL'd, by Julian Seward et al.
> ==27332== Using LibVEX rev 1804, a library for dynamic binary translation.
> ==27332== Copyright (C) 2004-2007, and GNU GPL'd, by OpenWorks LLP.
> ==27332== Using valgrind-3.3.0-Debian, a dynamic binary instrumentation
> framework.
> ==27332== Copyright (C) 2000-2007, and GNU GPL'd, by Julian Seward et al.
> ==27332== For more details, rerun with: -v
> ==27332==
> Running with 1*40 (== 40) tasks.
> ==27332== Thread 2:
> ==27332== Syscall param write(buf) points to uninitialised byte(s)
> ==27332==    at 0x4C1854B: (within /usr/lib/debug/libpthread-2.7.so)
> ==27332==    by 0x400C34: ready (hackbench.c:138)
> ==27332==    by 0x400C97: receiver (hackbench.c:182)
> ==27332==    by 0x4C113F6: start_thread (pthread_create.c:297)
> ==27332==    by 0x4EFD91C: clone (in /usr/lib/debug/libc-2.7.so)
> ==27332==  Address 0x558a09f is on thread 2's stack
> ==27332==
> ==27332== Thread 22:
> ==27332== Syscall param write(buf) points to uninitialised byte(s)
> ==27332==    at 0x4C1854B: (within /usr/lib/debug/libpthread-2.7.so)
> ==27332==    by 0x400C34: ready (hackbench.c:138)
> ==27332==    by 0x400D33: sender (hackbench.c:152)
> ==27332==    by 0x4C113F6: start_thread (pthread_create.c:297)
> ==27332==    by 0x4EFD91C: clone (in /usr/lib/debug/libc-2.7.so)
> ==27332==  Address 0x55da07f is on thread 22's stack
> ==27332==
> ==27332== Thread 40:
> ==27332== Syscall param write(buf) points to uninitialised byte(s)
> ==27332==    at 0x4C1854B: (within /usr/lib/debug/libpthread-2.7.so)
> ==27332==    by 0x400D6E: sender (hackbench.c:160)
> ==27332==    by 0x4C113F6: start_thread (pthread_create.c:297)
> ==27332==    by 0x4EFD91C: clone (in /usr/lib/debug/libc-2.7.so)
> ==27332==  Address 0x56220a0 is on thread 40's stack
> ==27332==
> ==27332== Thread 1:
> ==27332== Jump to the invalid address stated on the next line
> ==27332==    at 0x0: ???
> ==27332==    by 0x518702F: ???
> ==27332==    by 0xFFFFFFFF: ???
> ==27332==    by 0x518702F: ???
> ==27332==    by 0x2800000000: ???
> ==27332==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
> ==27332==
> ==27332== Process terminating with default action of signal 11 (SIGSEGV)
> ==27332==  Bad permissions for mapped region at address 0x0
> ==27332==    at 0x0: ???
> ==27332==    by 0x518702F: ???
> ==27332==    by 0xFFFFFFFF: ???
> ==27332==    by 0x518702F: ???
> ==27332==    by 0x2800000000: ???
> ==27332==
> ==27332== ERROR SUMMARY: 40041 errors from 4 contexts (suppressed: 8 from 1)
> ==27332== malloc/free: in use at exit: 11,420 bytes in 61 blocks.
> ==27332== malloc/free: 62 allocs, 1 frees, 11,692 bytes allocated.
> ==27332== For counts of detected errors, rerun with: -v
> ==27332== searching for pointers to 61 not-freed blocks.
> ==27332== checked 560,688 bytes.
> ==27332==
> ==27332== LEAK SUMMARY:
> ==27332==    definitely lost: 20 bytes in 1 blocks.
> ==27332==      possibly lost: 10,608 bytes in 39 blocks.
> ==27332==    still reachable: 792 bytes in 21 blocks.
> ==27332==         suppressed: 0 bytes in 0 blocks.
> ==27332== Rerun with --leak-check=full to see details of leaked memory.
> Segmentation fault
> 
> 
> 
> Best regards,
> --Edwin