Re: [patch 2.6.30-rc2 2/2] palm_bk3710: UDMA performance fix

[Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>]

On Tuesday 21 April 2009 12:02:22 Sergei Shtylyov wrote:
> David Brownell wrote:
> 
> > Fix UDMA throughput bug:  tCYC averages t2CYCTYP/2, but the code
> > previously assumed it was the same as t2CYCTYP.
> 
>     Wow, thanks for finding it!
>     IIUC however, this should have only affected UDMA writes, not reads 
> because on reads the device controls the strobe timing.
> 
> > (That is, it was using just one clock edge, not both.)
> 
>     There's no way only one clock edge could have been used since it would 
> have resulted in CRC errors, so this comment is not to the point.
> 
> > On one system this change increased throughput by almost 4x: UDMA/66
> > sometimes topped 23 MB/sec (on a drive known to do much better).  On
> > another system it was around a 10% win (UDMA/66 up to 7+ MB/sec).
> 
>     It's interesting that on my DM6467 EVM UDMA/66 reads topped at about 29-30 
> MB/s even without this patch (measuread with hdparm), and on DM6446 EVM they 
> were only slightly slower...
> 
> > The difference might be caused by the ratio between memory and IDE
> > clocks.  In the system with large speedup, this was exactly 2 (as a
> > workaround for a rev 1.1 silicon bug).  The other system used a more
> > standard ratio of 1.63 (and rev 2.1 silicon) ... clock domain synch
> > might have some issues, they're not unheard-of.
> 
>     Interesting...
> 
> > Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
> 
>     The patch itself is:
> 
> Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>

applied