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

[H . J . Lu]

On Thu, Dec 13, 2001 at 12:49:33AM +0100, Andrea Arcangeli wrote:
> 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

I applied all the way to 40_blkdev-pagecache-17 in 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.

That is why I said it was strange.

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

It blocks on read.

H.J.