netdev - Re: [PATCH v3 net-next 08/14] mlx4: use order-0 pages for RX

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Date:   Thu, 16 Feb 2017 14:03:55 -0500 (EST)
From:   David Miller <davem@...emloft.net>
To:     tom@...bertland.com
Cc:     tariqt@...lanox.com, edumazet@...gle.com, brouer@...hat.com,
        eric.dumazet@...il.com, alexander.duyck@...il.com,
        netdev@...r.kernel.org, kafai@...com, saeedm@...lanox.com,
        willemb@...gle.com, bblanco@...mgrid.com, ast@...nel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v3 net-next 08/14] mlx4: use order-0 pages for RX

From: Tom Herbert <tom@...bertland.com>
Date: Thu, 16 Feb 2017 09:05:26 -0800

> On Thu, Feb 16, 2017 at 5:08 AM, Tariq Toukan <tariqt@...lanox.com> wrote:
>>
>> On 15/02/2017 6:57 PM, Eric Dumazet wrote:
>>>
>>> On Wed, Feb 15, 2017 at 8:42 AM, Tariq Toukan <tariqt@...lanox.com> wrote:
>>>>
>>>> Isn't it the same principle in page_frag_alloc() ?
>>>> It is called form __netdev_alloc_skb()/__napi_alloc_skb().
>>>>
>>>> Why is it ok to have order-3 pages (PAGE_FRAG_CACHE_MAX_ORDER) there?
>>>
>>> This is not ok.
>>>
>>> This is a very well known problem, we already mentioned that here in the
>>> past,
>>> but at least core networking stack uses  order-0 pages on PowerPC.
>>
>> You're right, we should have done this as well in mlx4 on PPC.
>>>
>>> mlx4 driver suffers from this problem 100% more than other drivers ;)
>>>
>>> One problem at a time Tariq. Right now, only mlx4 has this big problem
>>> compared to other NIC.
>>
>> We _do_ agree that the series improves the driver's quality, stability,
>> and performance in a fragmented system.
>>
>> But due to the late rc we're in, and the fact that we know what benchmarks
>> our customers are going to run, we cannot Ack the series and get it
>> as is inside kernel 4.11.
>>
> You're admitting that Eric's patches improve driver quality,
> stability, and performance but you're not allowing this in the kernel
> because "we know what benchmarks our customers are going to run".
> Sorry, but that is a weak explanation.

I have to agree with Tom and Eric.

If your customers have gotten into the habit of using metrics which
actually do not represent real life performance, that is a completely
inappropriate reason to not include Eric's changes as-is.