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* question on the inner workings of NFS soft mount
@ 2007-07-26 22:29 Wim Colgate
  2007-07-26 22:39 ` Trond Myklebust
  0 siblings, 1 reply; 5+ messages in thread
From: Wim Colgate @ 2007-07-26 22:29 UTC (permalink / raw)
  To: nfs


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I was wondering if anyone could help me interpret the results of the
following experiment with regards to NFS softmount.

 

First a very brief description of my setup and test program:

 

I have a simple program that does a small, 512 byte, write to a file,
and print the success/failure of the IO plus the time the write took to
return, sleep one second, then loop back and write another - repeat
until ^C. The file it is writing to is on an NFS filer. During its
execution, I will disable the NFS service on the filer. The printfs of
success/failure are below.

 

The mount is SOFT: 

 

172.24.0.90:/vhd1 on /mnt/snp1 type nfs
(rw,soft,timeo=1,retrans=1,addr=172.24.0.90)

 

When I run one instance of the program here is the output:

 

# ./netwrite /mnt/snp1/foo2

write block 0 (succeeded): 0.006674 secs

write block 1 (succeeded): 0.001639 secs

write block 2 (succeeded): 0.001793 secs

write block 3 (succeeded): 0.001784 secs

write block 4 (succeeded): 0.004258 secs

write block 5 (succeeded): 0.002426 secs

write block 6 (succeeded): 0.001494 secs

write block 7 (succeeded): 0.001477 secs

write block 8 (succeeded): 0.001271 secs

write block 9 (failed): 3.00014 secs

write block 10 (failed): 3.00015 secs

write block 11 (failed): 6.00012 secs

write block 12 (failed): 12.0001 secs

write block 13 (failed): 24 secs

write block 14 (failed): 47.9999 secs

write block 15 (failed): 59.9996 secs

write block 16 (failed): 35 secs

write block 17 (failed): 59.9997 secs

write block 18 (failed): 59.9997 secs

write block 19 (failed): 59.9997 secs

write block 20 (failed): 9.00012 secs

 

 

I'm curious as to why the write failure times are all over the place.
Note the timeo and retrans are both set to 1. If I run two simultaneous
instances (to different files on the same filer), the times are also all
over the place - and go as high as two minutes (curiously twice the max
as one...).

 

I'm using the following version of linux:

 

Linux wims 2.6.18-8.1.8.el5.xs4.0.0b2.102.154xen #1 SMP Tue Jul 24
16:57:36 EDT 2007 i686 i686 i386 GNU/Linux

 

The program is pretty simple:

 

#define O_DIRECT        040000

 

#include <stdio.h>

#include <sys/types.h>

#include <sys/stat.h>

#include <fcntl.h>

#include <unistd.h>

#include <sys/select.h>

#include <errno.h>

#include <string.h>

#include <stdlib.h>

 

#include <sys/time.h>

 

#define ALIGN 512

#define SIZE 512

#define SEC_WAIT 1

 

main(int argc, char *argv[])

{

    int fd;

 

    int data=0;

    char *bufptr = 0;

    int result;

    struct timeval tim;

    struct timeval start;

    struct timeval end;

 

    if (argc != 2) {

        printf("usage: %s <filename>\n", argv[0]);

        goto done;

    }

 

    posix_memalign((void **)&bufptr, ALIGN, SIZE);

    if (!bufptr) {

        printf("failed to allocate %d bytes", SIZE);

        goto done;

    }

 

    fd = open(argv[1], O_RDWR | O_CREAT | O_DIRECT, 0777);

 

    if (!fd) {

        printf("failed to open %s for write, errno=%d\n", argv[1],
errno);

        goto done;

    }

 

    while (1) {

        ftime(&start);

        tim.tv_sec = SEC_WAIT;

        tim.tv_usec = 0;

        memset(bufptr, data, SIZE);

        gettimeofday(&start, 0);

        result = write(fd, bufptr, SIZE);

        data = (data+1) & 255;

        gettimeofday(&end, 0);

        printf("write block %d (%s): %g secs\n",

                                     data-1,

                                     result < 0 ? "failed" :
"succeeded",

                                     ((end.tv_sec*1000000 + end.tv_usec)
-

                                      (start.tv_sec*1000000 +
start.tv_usec))

                                      /1000000.0);

        select(0, 0, 0, 0, &tim);

    }

 

done:

    return 0;

}

 

Thanks,

 

Wim


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^ permalink raw reply	[flat|nested] 5+ messages in thread
end of thread, other threads:[~2007-07-26 22:43 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2007-07-26 22:29 question on the inner workings of NFS soft mount Wim Colgate
2007-07-26 22:39 ` Trond Myklebust
2007-07-26 22:39   ` Wim Colgate
2007-07-26 22:42     ` Trond Myklebust
2007-07-26 22:41   ` Wim Colgate

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