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@xxxxxxxxxxxxxxxxxxxxx> > > The patch itself is: > > Acked-by: Sergei Shtylyov <sshtylyov@xxxxxxxxxxxxx> applied -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
