netdev - Re: [PATCH v2 net-next 00/14] mlx4: order-0 allocations and page recycling

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Date:   Thu, 9 Feb 2017 08:56:25 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Tariq Toukan <ttoukan.linux@...il.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Martin KaFai Lau <kafai@...com>,
        Willem de Bruijn <willemb@...gle.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Brenden Blanco <bblanco@...mgrid.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH v2 net-next 00/14] mlx4: order-0 allocations and page recycling

On Thu, Feb 9, 2017 at 8:49 AM, Tariq Toukan <ttoukan.linux@...il.com> wrote:
>
>
> On 09/02/2017 6:44 PM, Eric Dumazet wrote:
>>
>> On Thu, Feb 9, 2017 at 8:41 AM, Tariq Toukan <ttoukan.linux@...il.com>
>> wrote:
>>>
>>> Hi Eric,
>>>
>>> Thanks again for your series.
>>>
>>> On 09/02/2017 3:58 PM, Eric Dumazet wrote:
>>>
>>> As mentioned half a year ago, we better switch mlx4 driver to order-0
>>> allocations and page recycling.
>>>
>>> This reduces vulnerability surface thanks to better skb->truesize
>>> tracking and provides better performance in most cases.
>>>
>>> v2 provides an ethtool -S new counter (rx_alloc_pages) and
>>> code factorization, plus Tariq fix.
>>>
>>> I see that you made significant changes to the previous series,
>>> especially
>>> patch 14 (RX CQE processing).
>>> Please notice that our work week has just finished here in Israel.
>>> I will review the series, especially the new patches (10 to 14), on
>>> Sunday.

> Default, out of box.

Well. Please report :

ethtool  -l eth0
ethtool -g eth0

>>
>>
>>> - TCP 16 streams at 1KB length.
>>
>> TCP does not really care, it coalesces all these into TSO skbs, full
>> size...
>
> But the kernel stack has to split it back accordingly in the receive side,
> no?

At 10Gbit or 40Gbit link speed, 16 TCP streams are sending 64KB TSO packets,
regardless of size of write() system calls.

Unless of course application uses write() with 1-byte, this might be
too expensive of course.