Steve, Do you use a 10k RPM SAS hard drive? Could you share that what test tools(or test cases) are you using to do the block IO test? We have a LSI SAS1068E chip and 10k RPM SAS hard drive in our lab. I'll find some time to reproduce the issue and do some investigation. Thanks, Forrest On 12/4/07, Steven Pratt <slpratt@xxxxxxxxxxxxxx> wrote: > I was doing some performance comparisons between the aic94xx sas adapter > and the mptsas (lsi1078 chip) and saw that performance was slightly > lower on lsi using the same drive. One thing I noticed the mptsas driver > was only setting sg_tablesize to 40 which restricts the maximum size of > the IO to 160kb. This is inefficient and so I changed it to 255 (max > value) for testing purposes. The results were not what I expected. > While CPU efficiency was improved at the larger block sizes (like I had > hopped), there were drastic improvements at small (<16k) block sizes > which is completely surprising). So I decided to see where all the time > was being spent. When doing oprofile, loss of idle ticks was confusing > things so I booted with idle=poll, and magically the original mptsas > driver now performs like the modified version at the small block sizes. > My suspicion is that we have some some sleep delay which is minimized by > going into poll mode, but I have no idea why changing the sg_tablesize > gives the same results regardless of poll mode. I should reiterate that > I am not talking about small difference. This is 2x performance at 1/3 cpu. > > Also, is there any reason we can't increase sg_tablesize for mptsas? > > Any thoughts or experiments to try are welcome. > Steve > - > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
