On Sun, May 14, 2006 at 12:13:21AM +1000, Nick Piggin wrote:
>
> OK, I got interested again, but can't get Val's ebizzy to give me
> a find_vma constrained workload yet (though the numbers back up
> my assertion that the vma cache is crap for threaded apps).
Hey Nick,
Glad to see you're using it! There are (at least) two ways to do what
you want:
1. Increase the number of threads - this gives you two vma's per
thread, one for stack, one for guard page:
$ ./ebizzy -t 100
2. Apply the patch at the end of this email and use -p "prevent
coalescing", -m "always mmap" and appropriate number of chunks,
size, and records to search - this works for me:
$ ./ebizzy -p -m -n 10000 -s 4096 -r 100000
The original program mmapped everything with the same permissions and
no alignment restrictions, so all the mmaps were coalesced into one.
This version alternates PROT_WRITE permissions on the mmap'd areas
after they are written, so you get lots of vma's:
val@goober:~/ebizzy$ ./ebizzy -p -m -n 10000 -s 4096 -r 100000
[2]+ Stopped ./ebizzy -p -m -n 10000 -s 4096 -r 100000
val@goober:~/ebizzy$ wc -l /proc/`pgrep ebizzy`/maps
10019 /proc/10917/maps
I haven't profiled to see if this brings find_vma to the top, though.
(The patch also moves around some other stuff so that options are in
alphabetical order; apparently I thought 's' came after 'r' and before
'R'...)
-VAL
--- ebizzy.c.old 2006-05-13 10:18:58.000000000 -0700
+++ ebizzy.c 2006-05-13 11:01:42.000000000 -0700
@@ -52,9 +52,10 @@
static unsigned int always_mmap;
static unsigned int never_mmap;
static unsigned int chunks;
+static unsigned int prevent_coalescing;
static unsigned int records;
-static unsigned int chunk_size;
static unsigned int random_size;
+static unsigned int chunk_size;
static unsigned int threads;
static unsigned int verbose;
static unsigned int linear;
@@ -76,9 +77,10 @@
"-m\t\t Always use mmap instead of malloc\n"
"-M\t\t Never use mmap\n"
"-n <num>\t Number of memory chunks to allocate\n"
+ "-p \t\t Prevent mmap coalescing\n"
"-r <num>\t Total number of records to search for\n"
- "-s <size>\t Size of memory chunks, in bytes\n"
"-R\t\t Randomize size of memory to copy and search\n"
+ "-s <size>\t Size of memory chunks, in bytes\n"
"-t <num>\t Number of threads\n"
"-v[v[v]]\t Be verbose (more v's for more verbose)\n"
"-z\t\t Linear search instead of binary search\n",
@@ -98,7 +100,7 @@
cmd = argv[0];
opterr = 1;
- while ((c = getopt(argc, argv, "mMn:r:s:Rt:vz")) != -1) {
+ while ((c = getopt(argc, argv, "mMn:pr:Rs:t:vz")) != -1) {
switch (c) {
case 'm':
always_mmap = 1;
@@ -111,19 +113,22 @@
if (chunks == 0)
usage();
break;
+ case 'p':
+ prevent_coalescing = 1;
+ break;
case 'r':
records = atoi(optarg);
if (records == 0)
usage();
break;
+ case 'R':
+ random_size = 1;
+ break;
case 's':
chunk_size = atoi(optarg);
if (chunk_size == 0)
usage();
break;
- case 'R':
- random_size = 1;
- break;
case 't':
threads = atoi(optarg);
if (threads == 0)
@@ -141,7 +146,7 @@
}
if (verbose)
- printf("ebizzy 0.1, Copyright 2006 Intel Corporation\n"
+ printf("ebizzy 0.2, Copyright 2006 Intel Corporation\n"
"Written by Val Henson <[email protected]\n");
/*
@@ -173,10 +178,11 @@
printf("always_mmap %u\n", always_mmap);
printf("never_mmap %u\n", never_mmap);
printf("chunks %u\n", chunks);
+ printf("prevent coalescing %u\n", prevent_coalescing);
printf("records %u\n", records);
printf("records per thread %u\n", records_per_thread);
- printf("chunk_size %u\n", chunk_size);
printf("random_size %u\n", random_size);
+ printf("chunk_size %u\n", chunk_size);
printf("threads %u\n", threads);
printf("verbose %u\n", verbose);
printf("linear %u\n", linear);
@@ -251,9 +257,13 @@
{
int i, j;
- for (i = 0; i < chunks; i++)
+ for (i = 0; i < chunks; i++) {
for(j = 0; j < chunk_size / record_size; j++)
mem[i][j] = (record_t) j;
+ /* Prevent coalescing by alternating permissions */
+ if (prevent_coalescing && (i % 2) == 0)
+ mprotect(mem[i], chunk_size, PROT_READ);
+ }
if (verbose)
printf("Wrote memory\n");
}
-
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