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Teach cat(1) and cp(1) to use a larger buffer if enough memory is present

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in the system. A simple heuristics is used to detect what is "enough"
memory: if number of physmem pages is greater than 32k (equalling 128 MB
on machines with 4 kB pages).

Typical immediate result of these changes is reduction in context switches
and the goal is to increase efficiency by using large buffers:
before: /usr/bin/time -hlp cat file1 > file2
...
       163  voluntary context switches
     11194  involuntary context switches
after: /usr/bin/time -hlp ./cat file1 > file2
...
       417  voluntary context switches
       272  involuntary context switches

Reviewed by:    hackers@ (no objections to earlier version of cat patch)
Approved by:    gnn (mentor)
MFC after:      4 months
This commit is contained in:
Ivan Voras 2008-10-30 14:05:57 +00:00
parent a1b9471a47
commit e9cbc9a770
2 changed files with 50 additions and 4 deletions
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23
bin/cat/cat.c
View File

@ -77,6 +77,17 @@ static void raw_cat(int);
static int udom_open(const char *path, int flags);
#endif
/* Memory strategy threshold, in pages: if physmem is larger then this, use a
* large buffer */
#define PHYSPAGES_THRESHOLD (32*1024)
/* Maximum buffer size in bytes - do not allow it to grow larger than this */
#define BUFSIZE_MAX (2*1024*1024)
/* Small (default) buffer size in bytes. It's inefficient for this to be
* smaller than MAXPHYS */
#define BUFSIZE_SMALL (MAXPHYS)
int
main(int argc, char *argv[])
{
@ -247,9 +258,17 @@ raw_cat(int rfd)
if (buf == NULL) {
if (fstat(wfd, &sbuf))
err(1, "%s", filename);
bsize = MAX(sbuf.st_blksize, 1024);
if (S_ISREG(sbuf.st_mode)) {
/* If there's plenty of RAM, use a large copy buffer */
if (sysconf(_SC_PHYS_PAGES) > PHYSPAGES_THRESHOLD)
bsize = MIN(BUFSIZE_MAX, MAXPHYS*8);
else
bsize = BUFSIZE_SMALL;
} else
bsize = MAX(sbuf.st_blksize,
(blksize_t)sysconf(_SC_PAGESIZE));
if ((buf = malloc(bsize)) == NULL)
err(1, "buffer");
err(1, "malloc() failure of IO buffer");
}
while ((nr = read(rfd, buf, bsize)) > 0)
for (off = 0; nr; nr -= nw, off += nw)

31
bin/cp/utils.c
View File

@ -57,10 +57,22 @@ __FBSDID("$FreeBSD$");
#define cp_pct(x, y) ((y == 0) ? 0 : (int)(100.0 * (x) / (y)))
/* Memory strategy threshold, in pages: if physmem is larger then this, use a
* large buffer */
#define PHYSPAGES_THRESHOLD (32*1024)
/* Maximum buffer size in bytes - do not allow it to grow larger than this */
#define BUFSIZE_MAX (2*1024*1024)
/* Small (default) buffer size in bytes. It's inefficient for this to be
* smaller than MAXPHYS */
#define BUFSIZE_SMALL (MAXPHYS)
int
copy_file(const FTSENT *entp, int dne)
{
static char buf[MAXBSIZE];
static char *buf = NULL;
static size_t bufsize;
struct stat *fs;
ssize_t wcount;
size_t wresid;
@ -174,8 +186,23 @@ copy_file(const FTSENT *entp, int dne)
} else
#endif
{
if (buf == NULL) {
/*
* Note that buf and bufsize are static. If
* malloc() fails, it will fail at the start
* and not copy only some files.
*/
if (sysconf(_SC_PHYS_PAGES) >
PHYSPAGES_THRESHOLD)
bufsize = MIN(BUFSIZE_MAX, MAXPHYS * 8);
else
bufsize = BUFSIZE_SMALL;
buf = malloc(bufsize);
if (buf == NULL)
err(1, "Not enough memory");
}
wtotal = 0;
while ((rcount = read(from_fd, buf, MAXBSIZE)) > 0) {
while ((rcount = read(from_fd, buf, bufsize)) > 0) {
for (bufp = buf, wresid = rcount; ;
bufp += wcount, wresid -= wcount) {
wcount = write(to_fd, bufp, wresid);