Date: Sun, 8 Oct 1995 07:15:43 +1000 From: Bruce Evans <bde@zeta.org.au> To: dennis@etinc.com, hackers@freebsd.org Subject: Re: VLB Disk Controllers Message-ID: <199510072115.HAA03150@godzilla.zeta.org.au>
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>Justin Gibbs says,
>>>Adaptec, Buslogic. Any possitive or negative comments on the drivers would
>>>be welcome.
>>>
>>>Dennis
>>
>>The 2842 seems to work well, supports tagged queuing and other advanced
>>SCSI II features that the buslogic (may be a driver limitation) does not.
>>The adaptec has much lower command overhead than the buslogic
That's not saying much. An IDE controller has a much lower command
overhead than the buslogic:
Buslogic BT44C on 486DX2/66 VLB TOSHIBA MK537FB (slow disk):
Output for disklatency /dev/rsd0:
Command overhead is 4741 usec (time_4096 = 5164, time_8192 = 5586)
transfer speed is 9.6955e+06 bytes/sec
Buslogic BT44C on 486DX2/66 VLB (QUANTUM XP34301 (fast disk):
output for disklatency /dev/rsd1:
Command overhead is 3968 usec (time_4096 = 4295, time_8192 = 4622)
transfer speed is 1.25286e+07 bytes/sec
Cheap IDE on 486DX/33 ISA SAMSUNG SHD-3212A (slow disk):
output for disklatency /dev/rwd0:
Command overhead is 573 usec (time_4096 = 2830, time_8192 = 5087)
transfer speed is 1.81489e+06 bytes/sec
A high command overhead causes slow file system operations for
everything except large i/o's.
What are the command overheads of other popular controllers?
Bruce
---
disklatency.c
---
#include <sys/types.h>
#include <sys/time.h>
#include <fcntl.h>
#include <stdio.h>
#include <unistd.h>
#define ITERATIONS 1000
static int syserror(const char *where);
static long timeit(int fd, char *buf, unsigned blocksize);
int main(int argc, char **argv)
{
char buf[2 * 4096];
int fd;
long time_4096;
long time_8192;
if (argc != 2)
{
fprintf(stderr, "usage: %s device\n", argv[0]);
exit(1);
}
fd = open(argv[1], O_RDONLY);
if (fd == -1)
syserror("open");
time_4096 = timeit(fd, buf, 4096);
time_8192 = timeit(fd, buf, 8192);
printf("Command overhead is %ld usec (time_4096 = %ld, time_8192 = %ld)\n",
(time_4096 - (time_8192 - time_4096)) / ITERATIONS,
time_4096 / ITERATIONS, time_8192 / ITERATIONS);
printf("transfer speed is %g bytes/sec\n",
4096 * ITERATIONS * 1000000.0 / (time_8192 - time_4096));
exit(0);
}
static int syserror(const char *where)
{
perror(where);
exit(1);
}
static long timeit(int fd, char *buf, unsigned blocksize)
{
struct timeval finish;
int i;
struct timeval start;
if (read(fd, buf, blocksize) != blocksize)
syserror("read");
if (gettimeofday(&start, (struct timezone *)NULL) != 0)
syserror("gettimeofday(start)");
for (i = 0; i < ITERATIONS; ++i)
{
if (lseek(fd, (off_t)0, SEEK_SET) == -1)
syserror("lseek");
if (read(fd, buf, blocksize) != blocksize)
syserror("read");
}
if (gettimeofday(&finish, (struct timezone *)NULL) != 0)
syserror("gettimeofday(finish)");
return (finish.tv_sec - start.tv_sec) * 1000000
+ finish.tv_usec - start.tv_usec;
}
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