Re: ECRC and Max Read Request Size

[Sinan Kaya <okaya@codeaurora.org>]

On 11/9/2015 2:15 PM, Bjorn Helgaas wrote:
>> I talked to our performance team. They are saying that max read
>> >request does not gain you much compared to max payload size single
>> >direction but it helps tremendously if you are moving data forth and
>> >back between the card. I don't have real numbers though.
> I'm not enough of a hardware or performance person to visualize how
> MRRS makes a tremendous difference in this situation.  Sample
> timelines comparing small vs. large MRRS would help everybody
> understand what's happening here.
>
> Bjorn

The LSI SAS 9211i card supports 4k maximum read request size. I manually 
forced this to 4k instead of the maximum payload size of the platform on 
both the host bridge and the endpoint.

I did a quick test with:
dd if=/dev/zero of=/dev/sda bs=1G count=1

It gave me %9 higher write performance.

-- 
Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a 
Linux Foundation Collaborative Project