Public bug reported:
The testing result of mbw tool installed by running “apt install mbw” is
shown below.
(tf2) bruce@P800002:~/tools/memtest/mbw_original$ mbw -a -n 1 1024
Long uses 8 bytes. Allocating 2*134217728 elements = 2147483648 bytes of
memory.
Using 262144 bytes as blocks for memcpy block copy test.
Getting down to business... Doing 1 runs per test.
0 Method: MEMCPY Elapsed: 0.20496 MiB: 1024.00000 Copy:
4996.097 MiB/s
0 Method: DUMB Elapsed: 0.11309 MiB: 1024.00000 Copy:
9055.136 MiB/s
0 Method: MCBLOCK Elapsed: 0.18077 MiB: 1024.00000 Copy:
5664.625 MiB/s
But the testing result from newest version of mbw which is downloaded
from github and built by myself is totally different with the former
one.
(tf2) bruce@P800002:~/tools/memtest/mbw_original$ ./mbw -a -n 1 1024
Long uses 8 bytes. Allocating 2*134217728 elements = 2147483648 bytes of
memory.
Using 262144 bytes as blocks for memcpy block copy test.
Getting down to business... Doing 1 runs per test.
0 Method: MEMCPY Elapsed: 0.11314 MiB: 1024.00000 Copy:
9050.334 MiB/s
0 Method: DUMB Elapsed: 0.20412 MiB: 1024.00000 Copy:
5016.632 MiB/s
0 Method: MCBLOCK Elapsed: 0.22396 MiB: 1024.00000 Copy:
4572.225 MiB/s
From the output of self-built mbw, you can see the speed of MEMCPY is
about 9050.334 MiB/s (much higher than the case of DUMB), but it is only
4996.097 MiB/s in the output of apt-installed mbw (much lower than the
case of DUMB).
After reading output of “git log -p mbw.c”, I believe apt repository is
still using a very old version of mbw, and unfortunately this version
involves a seriously issue which was fixed in the following changeset.
In this changeset, the code “if(type==1)” was changed to
“if(type==TEST_MEMCPY)” and the micro TEST_MEMCPY is 0. That means when
the “help” information(“-t1: dumb (b[i]=a[i] style) test”) shows number
1 case is DUMB, what it really did is MEMCPY.
Looking forward to fix this problem in apt repository by updating to
newest mbw in github.
diff --git a/mbw.c b/mbw.c
index 6251ea9..06a9d09 100644
--- a/mbw.c
+++ b/mbw.c
@@ -23,6 +23,11 @@
/* default block size for test 2, in bytes */
#define DEFAULT_BLOCK_SIZE 262144
+/* test types */
+#define TEST_MEMCPY 0
+#define TEST_DUMB 1
+#define TEST_MCBLOCK 2
+
/*
* MBW memory bandwidth benchmark
*
@@ -50,9 +55,9 @@ void usage()
printf("Options:\n");
printf(" -n: number of runs per test\n");
printf(" -a: Don't display average\n");
- printf(" -t0: memcpy test\n");
- printf(" -t1: dumb (b[i]=a[i] style) test\n");
- printf(" -t2 : memcpy test with fixed block size\n");
+ printf(" -t%d: memcpy test\n", TEST_MEMCPY);
+ printf(" -t%d: dumb (b[i]=a[i] style) test\n", TEST_DUMB);
+ printf(" -t%d: memcpy test with fixed block size\n",
TEST_MCBLOCK);
printf(" -b <size>: block size in bytes for -t2 (default: %d)\n",
DEFAULT_BLOCK_SIZE);
printf(" -q: quiet (print statistics only)\n");
printf("(will then use two arrays, watch out for swapping)\n");
@@ -100,13 +105,13 @@ double worker(unsigned long long asize, long *a,
long *b, int type, unsigned lon
/* array size in bytes */
unsigned long long array_bytes=asize*long_size;
- if(type==1) { /* memcpy test */
+ if(type==TEST_MEMCPY) { /* memcpy test */
/* timer starts */
gettimeofday(&starttime, NULL);
memcpy(b, a, array_bytes);
/* timer stops */
gettimeofday(&endtime, NULL);
- } else if(type==2) { /* memcpy block test */
+ } else if(type==TEST_MCBLOCK) { /* memcpy block test */
char* aa = (char*)a;
char* bb = (char*)b;
gettimeofday(&starttime, NULL);
@@ -117,7 +122,7 @@ double worker(unsigned long long asize, long *a,
long *b, int type, unsigned lon
bb=mempcpy(bb, aa, t);
}
gettimeofday(&endtime, NULL);
- } else { /* dumb test */
+ } else if(type==TEST_DUMB) { /* dumb test */
gettimeofday(&starttime, NULL);
for(t=0; t<asize; t++) {
b[t]=a[t];
@@ -142,13 +147,13 @@ double worker(unsigned long long asize, long *a,
long *b, int type, unsigned lon
void printout(double te, double mt, int type)
{
switch(type) {
- case 0:
+ case TEST_MEMCPY:
printf("Method: MEMCPY\t");
break;
- case 1:
+ case TEST_DUMB:
printf("Method: DUMB\t");
break;
- case 2:
+ case TEST_MCBLOCK:
printf("Method: MCBLOCK\t");
break;
}
ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: mbw 1.2.2-1build1
Uname: Linux 5.8.1inspurp8000 x86_64
ApportVersion: 2.20.9-0ubuntu7.24
Architecture: amd64
Date: Fri Jul 23 14:15:17 2021
Dependencies:
gcc-8-base 8.4.0-1ubuntu1~18.04
libc6 2.27-3ubuntu1.4
libgcc1 1:8.4.0-1ubuntu1~18.04
InstallationDate: Installed on 2021-07-07 (15 days ago)
InstallationMedia: Ubuntu 18.04.5 LTS "Bionic Beaver" - Release amd64
(20200806.1)
SourcePackage: mbw
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: mbw (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug bionic
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https://bugs.launchpad.net/bugs/1937338
Title:
wrong testing result of mbw
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