[dpdk-dev] [PATCH v4] ixgbe_pmd: enforce RS bit on every EOP descriptor for devices newer than 82598

[Brandeburg, Jesse]

+ixgbe developers.

-----Original Message-----
From: Vlad Zolotarov [mailto:vladz at cloudius-systems.com] 
Sent: Tuesday, October 27, 2015 11:48 AM
To: Thomas Monjalon; Ananyev, Konstantin; Zhang, Helin
Cc: dev at dpdk.org; Kirsher, Jeffrey T; Brandeburg, Jesse
Subject: Re: [dpdk-dev] [PATCH v4] ixgbe_pmd: enforce RS bit on every EOP descriptor for devices newer than 82598



On 10/27/15 20:09, Thomas Monjalon wrote:
> Any Follow-up to this discussion?
> Should we mark this patch as rejected?

Hmmm... This patch fixes an obvious spec violation. Why would it be 
rejected?

>
> 2015-08-24 11:11, Vlad Zolotarov:
>> On 08/20/15 18:37, Vlad Zolotarov wrote:
>>> According to 82599 and x540 HW specifications RS bit *must* be
>>> set in the last descriptor of *every* packet.
>>>
>>> Before this patch there were 3 types of Tx callbacks that were setting
>>> RS bit every tx_rs_thresh descriptors. This patch introduces a set of
>>> new callbacks, one for each type mentioned above, that will set the RS
>>> bit in every EOP descriptor.
>>>
>>> ixgbe_set_tx_function() will set the appropriate Tx callback according
>>> to the device family.
>> [+Jesse and Jeff]
>>
>> I've started to look at the i40e PMD and it has the same RS bit
>> deferring logic
>> as ixgbe PMD has (surprise, surprise!.. ;)). To recall, i40e PMD uses a
>> descriptor write-back
>> completion mode.
>>
>>   From the HW Spec it's unclear if RS bit should be set on *every* descriptor
>> with EOP bit. However I noticed that Linux driver, before it moved to
>> HEAD write-back mode, was setting RS
>> bit on every EOP descriptor.
>>
>> So, here is a question to Intel guys: could u, pls., clarify this point?
>>
>> Thanks in advance,
>> vlad
>
>