Re: Slow Disk I/O with QPS M3 80GB HD

[Andrea Arcangeli]

On Wed, Dec 12, 2001 at 03:38:06PM -0800, H . J . Lu wrote:
> H.J.
> ----
> 3 files on USB:
> 
> # ls -l
> total 5984
> -rwxr-xr-x    1 root     root      1991481 Dec  8 21:44 dsc00002.jpg
> -rwxr-xr-x    1 root     root      2432127 Dec  8 23:54 dsc00005.jpg
> -rwxr-xr-x    1 root     root      1675563 Dec  8 23:59 dsc00009.jpg
> 
> 1. 2.4.10-pre10
> 
> # time /bin/cp * /tmp/
> real    0m0.623s
> user    0m0.000s
> sys     0m0.100s
> 
> 2. 2.4.10-pre10aa1
> 
> # time /bin/cp * /tmp/
> real    0m8.952s
> user    0m0.000s
> sys     0m0.190s
> 
> 
> 3. 2.4.10-pre11
> 
> # time /bin/cp * /tmp/
> real    0m8.851s
> user    0m0.000s
> sys     0m0.170s

but the above have nothing to do with the blkdev-pagecache.
Blkdev-pagecache can matter only with blkdev accesses, blkdev-pagecache
cannot make any difference if the I/O passes through any fs (not via the
block_dev layer) like in the above case.

Can you try to take those cp under strace timestamp and see what's the
syscall that blocks?

Andrea