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Slow down the operation of background fsck so as to leave some disk

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bandwidth for other processes. Since the sleeping is done from
userland, this avoids the locking issues that affected the kernel
version.

The algorithm used here is to measure a moving average of the times
taken by a sample of read operations and then delay 1 in 8 reads
by 16 times the measured average. This should correspond to a factor
of 3 slowdown, but in practice the factor is larger (3.5 to 4) due
to hz rounding effects.

Reviewed by:	mckusick
Approved by:	re
This commit is contained in:
Ian Dowse 2002-12-07 21:40:31 +00:00
parent 16199bf2d3
commit 9d580d7c5f
1 changed files with 46 additions and 1 deletions
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47
sbin/fsck_ffs/fsutil.c
View file

@ -40,6 +40,7 @@ static const char rcsid[] =
#endif /* not lint */
#include <sys/param.h>
#include <sys/time.h>
#include <sys/types.h>
#include <sys/sysctl.h>
#include <sys/disklabel.h>
@ -62,7 +63,13 @@ static const char rcsid[] =
#include "fsck.h"
static void slowio_start(void);
static void slowio_end(void);
long diskreads, totalreads; /* Disk cache statistics */
struct timeval slowio_starttime;
int slowio_delay_usec = 10000; /* Initial IO delay for background fsck */
int slowio_pollcnt;
int
ftypeok(union dinode *dp)
@ -350,10 +357,15 @@ bread(int fd, char *buf, ufs2_daddr_t blk, long size)
offset = blk;
offset *= dev_bsize;
if (bkgrdflag)
slowio_start();
if (lseek(fd, offset, 0) < 0)
rwerror("SEEK BLK", blk);
else if (read(fd, buf, (int)size) == size)
else if (read(fd, buf, (int)size) == size) {
if (bkgrdflag)
slowio_end();
return (0);
}
rwerror("READ BLK", blk);
if (lseek(fd, offset, 0) < 0)
rwerror("SEEK BLK", blk);
@ -465,6 +477,39 @@ freeblk(ufs2_daddr_t blkno, long frags)
(void)pass4check(&idesc);
}
/* Slow down IO so as to leave some disk bandwidth for other processes */
void
slowio_start()
{
/* Delay one in every 8 operations by 16 times the average IO delay */
slowio_pollcnt = (slowio_pollcnt + 1) & 7;
if (slowio_pollcnt == 0) {
usleep(slowio_delay_usec * 16);
gettimeofday(&slowio_starttime, NULL);
}
}
void
slowio_end()
{
struct timeval tv;
int delay_usec;
if (slowio_pollcnt != 0)
return;
/* Update the slowdown interval. */
gettimeofday(&tv, NULL);
delay_usec = (tv.tv_sec - slowio_starttime.tv_sec) * 1000000 +
(tv.tv_usec - slowio_starttime.tv_usec);
if (delay_usec < 64)
delay_usec = 64;
if (delay_usec > 1000000)
delay_usec = 1000000;
slowio_delay_usec = (slowio_delay_usec * 63 + delay_usec) >> 6;
}
/*
* Find a pathname
*/