Re: ext3 performance inconsistencies, 2.4/2.6

From: Linus Torvalds
Date: Tue Nov 04 2003 - 14:37:49 EST

On Tue, 4 Nov 2003, Paul Venezia wrote:
> I've been running bonnie++ filesystems testing on an IBM x335 server
> recently. This box uses the MPT RAID controller, but I've disabled the
> RAID and am addressing the disks individually. I'm getting wildly
> different results between 2.4.20-20-9 (RedHat mod), 2.4.22 (stock), and
> 2.6.0-test9.

Interesting. The 2.4.22 sequential "per char" results are totally out of
line with anything else.

The thing is, the overhead for the per-char stuff really should be almost
all in user space unless I'm mistaken. It's just using getch/putch, no?

Which makes me suspect that either the libc does something different
depending on kernel version, _or_ 2.4.22 returns a different st_blksize
thing, causing stdio to use a different blocking size.

Have you tried stracing the "per char" parts of the benchmark to see what
the system call patterns are? That should show both effects.


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