DPDK patches and discussions
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From: Vlad Zolotarov <vladz@cloudius-systems.com>
To: "Ananyev, Konstantin" <konstantin.ananyev@intel.com>,
	 Olivier MATZ <olivier.matz@6wind.com>,
	"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH v6 3/3] ixgbe: Add LRO support
Date: Fri, 13 Mar 2015 14:12:47 +0200	[thread overview]
Message-ID: <5502D43F.3@cloudius-systems.com> (raw)
In-Reply-To: <2601191342CEEE43887BDE71AB977258213F5EC4@irsmsx105.ger.corp.intel.com>

On 03/13/15 13:28, Ananyev, Konstantin wrote:
> Hi Olivier,
>> -----Original Message-----
>> From: Olivier MATZ [mailto:olivier.matz@6wind.com]
>> Sent: Friday, March 13, 2015 9:08 AM
>> To: Vlad Zolotarov; Ananyev, Konstantin; dev@dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH v6 3/3] ixgbe: Add LRO support
>> Hi Vlad,
>> On 03/11/2015 05:54 PM, Vlad Zolotarov wrote:
>>>>>> About the existing RX/TX functions and PPC support:
>>>>>> Note that all of them were created before PPC support for DPDK was
>>>>>> introduced.
>>>>>> At that moment only IA was supported.
>>>>>> That's why in some places where you would expect to see 'mb()' there
>>>>>> are 'volatile' and/or ' rte_compiler_barrier' instead.
>>>>>> Why all that places wasn't updated when PPC support was added -
>>>>>> that's another question.
>>>>>>    From my understanding - with current implementation some of DPDK
>>>>>> PMDs RX/TX functions and  rte_ring wouldn't work correctly
>>>>> on PPC.
>>>>>> So, I suppose we need to decide for ourselves - do we really want to
>>>>>> support PPC and other architectures with non-IA memory
>>>>> model or not?
>>>>>> If not, then I think we don't need any mb()s inside recv_pkts_lro()
>>>>>> - just rte_compiler_barrier seems enough, and no point to
>>>>> complain about
>>>>>> it in comments.
>>>>>> If yes - then why to introduce a new function with a known potential
>>>>>> bug?
>>>>> In order to introduce a new function with the proper implementation or
>>>>> to fix any other places with the similar weakness I would need a proper
>>>>> tools like a proper platform-dependent barrier-macros similar to
>>>>> smp_Xmb() Linux macros that reduce to a compiler barrier where
>>>>> appropriate or to a proper memory fence where needed.
>>>> I understand that.
>>>> Let's add new macro for that: rte_smp_Xmb() or something,
>>>> so it would be just rte_compiler_barrier() for x86 and a proper mb()
>>>> for PPC.
>>> There was an idea to use the C11 built-in memory barriers. I suggest we
>>> open a separate discussion about that and add these and the appropriate
>>> fixes in a separate series. There are quite a few places to fix anyway,
>>> which are currently broken on PPC so this patch doesn't make things any
>>> worse. However adding a new memory barrier doesn't belong to an LRO
>>> functionality and thus to this series.
>> This is an interesting discussion. Just for reference, I submitted a
>> patch on this topic but it was probably too early as only Intel
>> architecture was supported at that time.
>> See http://dpdk.org/ml/archives/dev/2014-May/002597.html
> I do remember that conversation :)
> At that moment, as nothing except IA wasn't supported, I feel it was not needed.
> Though now, if we do want to support PPC and other architectures with weak memory model,
> I think we do need to introduce some platform dependent set of Xmb() macros.
> See http://dpdk.org/ml/archives/dev/2014-October/006729.html
> Actually while thinking about it once again:
> Is there any good use for rte_compiler_barrier() for PPC memory model?
> I can't think about any.
> So I wonder can't we just make for PPC:
>   #define rte_compiler_barrier    rte_mb
> While keeping it as it is for IA.
> Would save us from searching/replacing though all the code.

I wonder why should we invent a wheel? Like Avi has proposed we may use 
the existing standard C library primitives for that. See this 
http://en.cppreference.com/w/c/atomic. I don't know what's the state of 
icc in this area though... ;)


  * Zero maintenance.
  * Multi-platform support.
  * It seems that this is the direction the industry is going to (as
    opposed to the discussed above mb(), rmb(), wmb() model).


  * The model is a bit different from what most of the kernel
    programmers used to.
  * The current code adaptation would be a bit more painful (due to
    first "cons").

I think this could be a very nice move. For a user space for sure. The 
open question is a KNI component. I don't know how much code is shared 
between kernel and user space DPDK code but if there isn't much - then 
we may still go for a built-in C atomics primitives in a user space and 
do whatever we choose in the KNI...

>   Konstantin
>> Regards,
>> Olivier

  reply	other threads:[~2015-03-13 12:12 UTC|newest]

Thread overview: 18+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-03-09 19:07 [dpdk-dev] [PATCH v6 0/3]: Add LRO support to ixgbe PMD Vlad Zolotarov
2015-03-09 19:07 ` [dpdk-dev] [PATCH v6 1/3] ixgbe: Cleanups Vlad Zolotarov
2015-03-09 20:15   ` Ananyev, Konstantin
2015-03-09 19:07 ` [dpdk-dev] [PATCH v6 2/3] ixgbe: Code refactoring Vlad Zolotarov
2015-03-09 19:07 ` [dpdk-dev] [PATCH v6 3/3] ixgbe: Add LRO support Vlad Zolotarov
2015-03-10  0:30   ` Ananyev, Konstantin
2015-03-10 13:22     ` Vlad Zolotarov
2015-03-10 20:09       ` Ananyev, Konstantin
2015-03-10 21:36         ` Vlad Zolotarov
2015-03-11 16:32           ` Ananyev, Konstantin
2015-03-11 16:54             ` Vlad Zolotarov
2015-03-13  9:07               ` Olivier MATZ
2015-03-13 11:28                 ` Ananyev, Konstantin
2015-03-13 12:12                   ` Vlad Zolotarov [this message]
2015-03-10 17:51     ` Vlad Zolotarov
2015-03-16 18:26   ` Vlad Zolotarov
2015-03-18  0:31     ` Ananyev, Konstantin
2015-03-18 10:29       ` Vlad Zolotarov

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