Re: [PATCH] readahead: initial method - expected read size - fix fastcall

[Voluspa <lista1@comhem.se>]

On Tue, 6 Jun 2006 10:26:06 +0800 Fengguang Wu wrote:
> On Mon, Jun 05, 2006 at 03:17:20AM +0200, Voluspa wrote:
> > Patch:
> > http://web.comhem.se/~u46139355/storetmp/adaptive-readahead-v14-linux-2.6.17-rc5-git-updated-june-04-2006.patch
> 
> It seems that the patch has some problem:
[...]
> The above statements was displaced, rendering the if() clause to fail all the time.
> That defeats the small file optimization, for ra_thrash_bytes will remain small.

Which rendered all my testing invalid. Nice... It came about with the
update-01to04of04 and must have elicited a "fuzz" that I neglected to
check. 

Sorry to have caused you grief and extra work, Wu. I can only point 
towards the _Caveat and preemptive Mea Culpa_.

> Voluspa, I attached an updated patch, including two more performance tunings.
> Please take it when you find time to do more benchmarks, thanks.
> 
> I'd suggest that you(and other kind people interested in testing it out) to run
>         blockdev --setra 2048 /dev/[sda/sda1/...]
> before each benchmark to ensure fairness and simplicity of analysis, thanks.

I'm in the process of writing up a new report after having tested for ca 6
hours straight (repenting mood). Will post in the original thread:

Adaptive Readahead V14 - statistics question...
http://marc.theaimsgroup.com/?t=114893205000004&r=1&w=2

The subject has a 'higher profile' than this one and might pull in future
testers.

Note to Andrew; Revised Conclusion: On _this_ machine, with _these_ operations,
Adaptive Readahead in its current incarnation and default settings is a slight
_loss_. However, if the readahead size is lowered from 2048 to 256, it becomes
a slight _gain_ or at least stays in parity with normal readahead.

Mvh
Mats Johannesson
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