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SubjectRe: Why is 2.4.32 four times faster than 2.6.14.6??
Hi Grant,

On Sun, Jan 08, 2006 at 06:28:53PM +1100, Grant Coady wrote:
> On Sun, 8 Jan 2006 07:58:09 +0100, Markus Rechberger <mrechberger@gmail.com> wrote:
>
> >Were there any other processes running during the test?
> box runs same config both kernels: the usual light load ~100% idle ;)
> >what does "vmstat 1" show up during the test?
>
> grant@deltree:~$ uname -r
> 2.6.14.6a
> grant@deltree:~$ vmstat 1
> procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
> r b swpd free buff cache si so bi bo in cs us sy id wa
> [...]
> 0 0 0 63800 11520 32352 0 0 0 0 110 18 0 0 100 0
> 0 0 0 63800 11520 32352 0 0 0 0 106 17 1 0 99 0
> 3 0 0 63560 11520 32352 0 0 0 0 346 502 22 9 69 0
> 1 0 0 63560 11520 32352 0 0 0 0 1057 1987 59 41 0 0
> 1 0 0 63560 11520 32352 0 0 0 0 1062 2011 59 41 0 0
> 1 0 0 63560 11520 32352 0 0 0 0 1053 2001 50 50 0 0
> 1 0 0 63500 11596 32352 0 0 0 136 1054 1974 61 39 0 0
> 1 0 0 63500 11596 32352 0 0 0 0 1040 1978 50 50 0 0
> 0 0 0 63620 11596 32352 0 0 0 0 799 1425 45 27 29 0
> 0 0 0 63620 11596 32352 0 0 0 0 104 12 0 0 100 0
> 0 0 0 63620 11596 32352 0 0 0 0 103 10 0 0 100 0
>
> grant@deltree:~$ uname -r
> 2.4.32-hf32.1
> grant@deltree:~$ vmstat 1
> procs -----------memory---------- ---swap-- -----io---- --system-- ----cpu----
> r b swpd free buff cache si so bi bo in cs us sy id wa
> [...]
> 0 0 0 83192 6532 21404 0 0 0 0 104 12 0 1 99 0
> 0 0 0 83152 6572 21404 0 0 0 80 116 24 0 1 99 0
> 1 0 0 82952 6572 21404 0 0 0 0 168 130 6 5 89 0
> 2 0 0 82952 6572 21404 0 0 0 0 667 1019 65 35 0 0
> 0 0 0 83152 6572 21404 0 0 0 0 297 378 41 10 49 0
> 0 0 0 83152 6572 21404 0 0 0 0 104 9 0 1 99 0
> 0 0 0 83064 6656 21404 0 0 0 304 169 121 0 1 99 0
> 0 0 0 83064 6656 21404 0 0 0 0 137 42 0 2 98 0

It's rather strange that 2.6 *eats* CPU apparently doing nothing ! At first
I thought about a PIO/DMA problemn but we can clearly see that there's no
IO in on both vmstat. Could you please retest :
- without the pipe (remove '| cut ...') to avoid inter-process
communications
- with cat instead of grep to ensure you don't spend time processing
anything

You should be able to find one simple pattern which makes the problem
appear/disappear on 2.6. At least, 'cat x.log >/dev/null' should not
take time or that time should be spent in I/O. I remember an old test
I did a long time ago which behaved badly on 2.6, it consisted in lots
of pipes (eg: dd bs=1 | dd bs=1 |...). May be you're on a simplified
form of this.

> --
> Thanks,
> Grant.
> http://bugsplatter.mine.nu/

Cheers,
Willy

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