On Wednesday 30 April 2003 00:22, Edward J. Lee wrote:
> Hi YAFFSers, been a while.
>
> No problems were found using YAFFS but now I'm suffering by extra-slow
> performance.
> My program formerly stored user configurations in HDDs, now we're
> storing it in
> NAND. As the saving part involves a great deal of fopen()s, fseek()s,
> fwrite()s, and etc.,
> It took a while (but not TOO much) storing it in HDDs. But on YAFFS, the
> time
> grew catastrophically, and it takes approx. 15 secs saving 62KB!
>
> Does anyone have any ideas that might help me out?

This is the sort of thing that will happen if your writes and reads cannot 
use the caching effectively.

YAFFS works directly on the flash with no buffering between the file system 
and the flash. There is, however, buffering in the form of the normal kernel 
cache between YAFFS and the applicaion.
The caching is flushed out by any close or flush. On a close or flush, the 
file's ObjectHeader will also be updated, costing another page write.

eg. writing a 64kB file as follows would be very slow:

for(i = 0; i < 64000; i++)
{
 h = open("xx",...O_APPEND);
write(h,&b,1);
close(h);
}

would cost two page writes for every useful byte written.

I expect you're not being as cruel as this, but check for places where you 
are doing unnecessary flushes and closes. 

If you suspect the Linux cache might not be effective for your purposes (or 
would like to play :-)), you might also try the caching built in to YAFFS. 
This caching is normally used only by YAFFS direct and WinCE (which do not 
have OS-level caching).

 This can be enabled by adding the line 
  dev->nShortOpCaches=10; // or some number <=20;
somewhere around line 1248 in yaffs_fs.c

On WinCE devices, this vastly improved situations where short writes were 
being used (by a factor of 15 or so).

-- Charles






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