netdev - Re: [PATCH net-next] mlx4: Better use of order-0 pages in RX path

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Message-ID: <20170313234050.GA82263@ast-mbp.thefacebook.com>
Date:   Mon, 13 Mar 2017 16:40:51 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...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>,
        Saeed Mahameed <saeedm@...lanox.com>,
        Willem de Bruijn <willemb@...gle.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Alexander Duyck <alexander.duyck@...il.com>
Subject: Re: [PATCH net-next] mlx4: Better use of order-0 pages in RX path

On Mon, Mar 13, 2017 at 04:28:04PM -0700, Eric Dumazet wrote:
> On Mon, Mar 13, 2017 at 4:21 PM, Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > is it once in the beginning only? If so then why that
> > 'if (!ring->page_cache.index)' check is done for every packet?
> 
> 
> 
> You did not really read the patch, otherwise you would not ask these questions.

please explain. I see
+  if (!ring->page_cache.index) {
+          npage = mlx4_alloc_page(priv, ring,
which is done for every packet that goes via XDP_TX.

> Test it, and if you find a regression, shout loudly.

that's not how it works. It's a job of submitter to prove
that additional code doesn't cause regressions especially
when there are legitimate concerns.