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 I have recently taken the plunge to update to a newer version of the kernel starting at 2.6.32 (also tried 2.6.33) and what I am seeing writes speeds drop to about 18 MBps peak with large jumps going from 8 MBps-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-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
