Re: [PATCH 2.4] jffs2 aligment problems

[Thomas Gleixner]

On Monday 07 June 2004 22:54, Linus Torvalds wrote:
> On Mon, 7 Jun 2004, David Woodhouse wrote:
> > On Mon, 2004-06-07 at 12:22 -0700, Linus Torvalds wrote:
> > > I don't see it as a correctness issue, I see it as a performance issue.
> >
> > In the case in question it's very much _not_ a performance issue. We're
> > writing a buffer to FLASH memory. The time it takes to read the word
> > from RAM is entirely lost in the noise compared with the time it takes
> > to write it to the flash.
>
> Not if you have to take an alignment fault, which is easily several
> thousand cycles.
>
> Think of "get_unaligned()" as a worst-case limiter. It can make the best
> case be worse on architectures where it matters, but it can make the worst
> case go from thousands of cycles to just single cycles.
>
> And your flash isn't _that_ slow. Thousands of cycles that can't even
> overlap with any flash IO _does_ show up.

Not the IO write to the FLASH is the slow and noisy part, its the programming 
of the FLASH after writing the data which blocks for a non deteministic time 
in the range of milliseconds.
So we did not care if it took ms + x Âs due to an alignement trap

-- 
Thomas
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________________________________________________________________________
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