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

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Date:   Mon, 13 Feb 2017 15:47:23 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Martin KaFai Lau <kafai@...com>,
        Saeed Mahameed <saeedm@...lanox.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 v3 net-next 08/14] mlx4: use order-0 pages for RX

On Mon, Feb 13, 2017 at 3:29 PM, Eric Dumazet <edumazet@...gle.com> wrote:
> On Mon, Feb 13, 2017 at 3:26 PM, Alexander Duyck
> <alexander.duyck@...il.com> wrote:
>
>>
>> Odds are for a single TCP flow you won't notice.  This tends to be
>> more of a small packets type performance issue.  If you hammer on he
>> Rx using pktgen you would be more likely to see it.
>>
>> Anyway patch looks fine from a functional perspective so I am okay
>> with it.  The page count bulking is something that can be addressed
>> later.
>
> Well, if we hammer enough, pages are not recycled because we cycle
> through RX ring buffer too fast.
>
> This might be different for PowerPC though, because of its huge PAGE_SIZE.

Actually it depends on the use case.  In the case of pktgen packets
they are usually dropped pretty early in the receive path.  Think
something more along the lines of a TCP syn flood versus something
that would be loading up a socket.

- Alex