Date:	Thu, 26 Mar 2015 18:02:26 +0200
From:	Vlad Zolotarov <vladz@...udius-systems.com>
To:	Alexander Duyck <alexander.h.duyck@...hat.com>,
	"Tantilov, Emil S" <emil.s.tantilov@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
	"avi@...udius-systems.com" <avi@...udius-systems.com>,
	"gleb@...udius-systems.com" <gleb@...udius-systems.com>,
	"Skidmore, Donald C" <donald.c.skidmore@...el.com>
Subject: Re: [PATCH net-next v6 4/7] ixgbevf: Add a RETA query code



On 03/26/15 17:59, Alexander Duyck wrote:
>
> On 03/26/2015 08:10 AM, Vlad Zolotarov wrote:
>>
>>
>> On 03/26/15 16:40, Alexander Duyck wrote:
>>>
>>> On 03/26/2015 02:35 AM, Vlad Zolotarov wrote:
>>>>
>>>>
>>>> On 03/25/15 23:04, Alexander Duyck wrote:
>>>>>
>>>>> On 03/25/2015 01:17 PM, Vlad Zolotarov wrote:
>>>>>>
>>>>>>
>>>>>> On 03/25/15 20:35, Tantilov, Emil S wrote:
>>>>>>>> -----Original Message-----
>>>>>>>> From: Vlad Zolotarov [mailto:vladz@...udius-systems.com]
>>>>>>>> Sent: Wednesday, March 25, 2015 2:28 AM
>>>>>>>> Subject: Re: [PATCH net-next v6 4/7] ixgbevf: Add a RETA query 
>>>>>>>> code
>>>>>>>
>>>>>>
>>>
>
> <snip>
>
>>>
>>>>
>>>>>
>>>>>>
>>>>>> The user should actually not query the indirection table and a 
>>>>>> hash key too often. And if he/she does - it should be his/her 
>>>>>> problem.
>>>>>> However, if like with the ixgbevf_set_num_queues() u insist on 
>>>>>> your way of doing this (on caching the indirection table and hash 
>>>>>> key) - then please let me know and I will add it. Because, 
>>>>>> frankly, I care about the PF part of this series much more than 
>>>>>> for the VF part... ;)
>>>>>
>>>>> I would say you don't need to cache it, but for 82599 and x540 
>>>>> there isn't any need to store more than 3 bits per entry, 384b, or 
>>>>> 12 DWORDs for the entire RETA of the VF since the hardware can 
>>>>> support at most 8 queues w/ SR-IOV. Then you only need one message 
>>>>> instead of 3 which will reduce quite a bit of the complication 
>>>>> with all of this.
>>>>>
>>>>> Also it might make more sense to start working on displaying this 
>>>>> on the PF before you start trying to do this on the VF. As far as 
>>>>> I know ixgbe still doesn't have this functionality and it would 
>>>>> make much more sense to enable that first on ixgbe before you 
>>>>> start trying to find a way to feed the data to the VF.
>>>>
>>>> Let's agree on the next steps:
>>>>
>>>> 1. I'll reduce the series scope to 82599 and x540 devices.
>>>
>>> For mailbox implementation that is okay, my advice for the x550 
>>> would be to just read the registers.  They should already be defined 
>>> in the driver so it is just a matter of reversing the process for 
>>> writing the RETA.  You should have a solid grasp of that once you 
>>> implement the solution for the PF.
>>
>> The problem is that I have no means to validate the solution - I have 
>> only x540 devices (nor specs). I'd prefer not to work in darkness and 
>> let u, guys, do it...
>
> If it helps the specs for the x540 can be found at 
> http://www.intel.com/content/www/us/en/network-adapters/10-gigabit-network-adapters/ethernet-x540-datasheet.html. 
> Section 8 has a full list of the register definitions.

I meant I don't have x550 specs - I'm working against x540 spec quite 
intensively... ;)

>
> All the code you need should already be stored in ixgbe_setup_reta and 
> ixgbe_setup_vfreta.  If you do it right you shouldn't even need to 
> read the hardware.  Odds are you could generate it in software and 
> that is what you would be accessing on the PF.  After all, if at some 
> point you reset the hardware you would need to restore it from 
> software wouldn't you, and since the table is static for now you 
> should be able to calculate the value without need of reading a 
> register.  If at some point in the future you can change the table 
> then it means a copy has to be maintained in kernel memory and at that 
> point you could use that for the data you would be sending to the VF.
>
>>>
>>>> 4. I won't implement the caching of the indirection and RSS hash key
>>>>    query results in the VF level.
>>>
>>> The idea with caching is to keep the number of messages across the 
>>> mailbox to a minimum.  Compressing it down to 3 bits per entry will 
>>> help some, but I am not sure if that is enough to completely 
>>> mitigate the need for caching.  For now though the caching isn't a 
>>> must-have, and it won't be needed for x550 since it can access the 
>>> table directly.  The main thing I would recommend keeping an eye on 
>>> would be how long it will take to complete the messages necessary to 
>>> get the ethtool info.  If there are any scenarios where things take 
>>> more than 1 second then I would say we are taking too long and we 
>>> would have to look into caching because we want to avoid holding the 
>>> rtnl lock for any extended period of time.
>>
>> I've described the limitations the caching approach imposes above. I 
>> suggest we follow your approach here - solve the problems when they 
>> arrive. ;) I haven't succeeded to make it take as long as even near 
>> one second.
>>
>>>
>>> My advice is get the PF patches in first, then we can look at trying 
>>> to get feature parity on the VF.
>>
>> "feature parity on the VF"?
>
> Get "ethtool -x/X" working on the PF, and then get it working on the 
> VF.  That way it makes for very simple verification as you can inspect 
> that the PF and VF tables are consistent.  As I said if nothing else 
> you can probably take a look at the igb driver to see how this was 
> done on the 1Gbps Intel hardware.
>
>>
>> I'll send the patches later today. I'll incorporate the new PF code 
>> into the existing series.
>
> You might want to break things out into a couple series of patches. Do 
> the PF driver first just to make sure you have an understanding of 
> what you expect, think of it as a proof of concept if nothing else for 
> how you want the VF to function, then submit the VF series as a 
> separate patch set and include the mailbox API changes.
>
> - Alex
>

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