Re: [PATCH] updated reiser4 - reduced cpu usage for writes by writing more than 4k at a time (has implications for generic write code and eventually for the IO layer)

[Jens Axboe]

On Wed, May 24 2006, Hans Reiser wrote:
> Tom Vier wrote:
> 
> >On Tue, May 23, 2006 at 01:14:54PM -0700, Hans Reiser wrote:
> >  
> >
> >>underlying FS can be improved.  Performance results show that the new
> >>code consumes  40% less CPU when doing "dd bs=1MB ....." (your hardware,
> >>and whether the data is in cache, may vary this result).  Note that this
> >>has only a small effect on elapsed time for most hardware.
> >>    
> >>
> >
> >Write requests in linux are restricted to one page?
> >
> >  
> >
> It may go to the kernel as a 64MB write, but VFS sends it to the FS as
> 64MB/4k separate 4k writes.

Nonsense, there are ways to get > PAGE_CACHE_SIZE writes in one chunk.
Other file systems have been doing it for years.

-- 
Jens Axboe