Re: [dpdk-dev] i40e: Steps and required configurations of how to achieve the best performance!

[David Marchand <david.marchand@6wind.com>]

On Wed, Sep 17, 2014 at 10:50 AM, Zhang, Helin <helin.zhang@intel.com>
wrote:

>  For the ‘extended tag’, it was defined in PCIe spec, but actually not
> all BIOS implements it. Enabling it in BIOS or at runtime are two choices
> of doing the same thing. I don’t think it can be configured per PCI device
> in BIOS, so we don’t need to do that per PCI device in DPDK. Right?
> Actually we don’t want to touch PCIe settings in DPDK code, that’s why we
> want to let BIOS config as it is by default. If no better choice, we can do
> it in DPDK by changing configurations.
>

- Ok, then if we can make a runtime decision (at dpdk level), there is no
need for bios configuration and there is no need for a build option.
Why don't we get rid of this option ?

As far as the per-device runtime configuration is concerned, I want to make
sure this pci configuration will not break other "igb_uio" pci devices.
If Intel can tell for sure this won't break other devices, then fine, we
can go and enable this for all "igb_uio" pci devices.


- By the way, there is also the CONFIG_MAX_READ_REQUEST_SIZE option that
seems to be disabled (or at least its value 0 seems to tell so).
What is its purpose ?



>
> For ‘CONFIG_RTE_LIBRTE_I40E_16BYTE_RX_DESC=n’ by default, we want to
> support 32 bytes rx descriptors by default. Two reasons:
>
> One is 32 bytes rx descriptors can provide more powerful features, and
> more offload features.
>
> The other is Linux PF host use 32 bytes rx descriptor by default which
> might not able to be changed, to support Linux PF host, it would be better
> to use 32 bytes rx descriptors in DPDK VF by default.
>

Ok, good to know.

Thanks.

-- 
David Marchand