Zhao Forrest wrote:
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.
I've been using 10k and 15k drives (although these particular tests were
from 15k). I've been mostly using an internal IO tool, but this is
easily reproducible with dd using the iflag=direct to force ODIRECT.
Steve
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
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