El Thu, 16 Sep 2010 17:30:51 -0600 "Joshua Hintze" <joshh@xxxxxxxxx> escribió: [ Just CC linux-ide ] > Hello, > > I've been digging into this for a couple weeks now. I have an embedded board > that runs Linux Kernel 2.6.10 that is connected to a SSD over a PATA > connection. Data is transferred using UDMA4 speeds and I get a nice > sustained write speed of about 20 MBps which is adequate for us. > > I have recently taken the plunge to update to a newer version of the kernel > starting at 2.6.32 (also tried 2.6.33) and what I am seeing writes speeds > drop to about 18 MBps peak with large jumps going from 8 MBps->16 MBs for > sustained throughput. > > I decided to read up on the ATA specification and I connected a logic > analyzer to the PATA bus and here is what is happening...after a large chunk > of data is written to the device, instead of the device pausing the transfer > by asserting DDMARDY it actual initiates a device data-out termination by > pulling DMARQ low. > > The old kernel 2.6.10 responds to this by strobing the STOP line 8 times > within 800uS and the device releases DMARQ shortly afterwards. On the newer > kernels the strobing of the STOP line takes near 8mS of time. Since the hard > drive only release DMARQ after this 8 pulse strobe I believe this is the > cause of the slower write speeds on the newer kernels. This whole process > happens thousands of times when writing megs of data. So those extra 7mS > begin to add up fast. > > My problem is I've been digging through the ide.c/ide-dma.c and other code > but I'm not exactly sure where the code would jump to upon a device > initiated termination on a data-out dma transfer. > > My guess is ide_dma_intr(...). Is this correct? > > Any other areas I could look at? > > Thanks in advance. > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- 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
