netdev - Re: [bpf-next V2 PATCH 10/15] xdp: rhashtable with allocator ID to pointer mapping

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Message-ID: <01481dbe-ed95-dd2e-67f7-1543d75cc138@redhat.com>
Date:   Thu, 22 Mar 2018 10:16:47 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     netdev@...r.kernel.org,
        BjörnTöpel <bjorn.topel@...el.com>,
        magnus.karlsson@...el.com, eugenia@...lanox.com,
        John Fastabend <john.fastabend@...il.com>,
        Eran Ben Elisha <eranbe@...lanox.com>,
        Saeed Mahameed <saeedm@...lanox.com>, galp@...lanox.com,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Tariq Toukan <tariqt@...lanox.com>
Subject: Re: [bpf-next V2 PATCH 10/15] xdp: rhashtable with allocator ID to
 pointer mapping



On 2018年03月20日 22:27, Jesper Dangaard Brouer wrote:
> On Tue, 20 Mar 2018 10:26:50 +0800
> Jason Wang <jasowang@...hat.com> wrote:
>
>> On 2018年03月19日 17:48, Jesper Dangaard Brouer wrote:
>>> On Fri, 16 Mar 2018 16:45:30 +0800
>>> Jason Wang <jasowang@...hat.com> wrote:
>>>   
>>>> On 2018年03月10日 00:07, Jesper Dangaard Brouer wrote:
>>>>> On Fri, 9 Mar 2018 21:07:36 +0800
>>>>> Jason Wang <jasowang@...hat.com> wrote:
>>>>>      
>>>>>>>>> Use the IDA infrastructure for getting a cyclic increasing ID number,
>>>>>>>>> that is used for keeping track of each registered allocator per
>>>>>>>>> RX-queue xdp_rxq_info.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Jesper Dangaard Brouer<brouer@...hat.com>
>>>>>>>> A stupid question is, can we manage to unify this ID with NAPI id?
>>>>>>> Sorry I don't understand the question?
>>>>>> I mean can we associate page poll pointer to napi_struct, record NAPI id
>>>>>> in xdp_mem_info and do lookup through NAPI id?
>>>>> No. The driver can unreg/reg a new XDP memory model,
>>>> Is there an actual use case for this?
>>> I believe this is the common use case.  When attaching an XDP/bpf prog,
>>> then the driver usually want to change the RX-ring memory model
>>> (different performance trade off).
>> Right, but a single driver should only have one XDP memory model.
> No! -- a driver can have multiple XDP memory models, based on different
> performance trade offs and hardware capabilities.
>
> The mlx5 (100Gbit/s) driver/hardware is a good example, which need
> different memory models.  It already support multiple RX memory models,
> depending on HW support.

So let me correct my question, not familiar with mlx5e driver but if I 
understand correctly, driver (mlx5) will not change memory model during 
runtime for each NAPI. So NAPI id still work in this case?

> So, I predict that we hit at performance
> limit around 42Mpps on PCIe (I can measure 36Mpps), this is due to
> PCI-express translations/sec limit.  The mlx5 HW supports a compressed
> descriptor format which deliver packets in several pages (based on
> offset and len), thus lowering the needed PCIe transactions.  The
> pitfall is that this comes tail room limitations, which can be okay if
> e.g. the users use-case does not involve cpumap.
>
> Plus, when a driver need to support AF_XDP zero-copy, that also count
> as another XDP memory model...

Yes or TAP zero-copy XDP. But it looks to me that we don't even need to 
care about the recycling here since the pages belongs to userspace.

Thanks