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

From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Eric Dumazet <edumazet@google.com>
Cc: "David S . Miller" <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
	Tariq Toukan <tariqt@mellanox.com>,
	Saeed Mahameed <saeedm@mellanox.com>,
	Willem de Bruijn <willemb@google.com>,
	Alexei Starovoitov <ast@kernel.org>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	Alexander Duyck <alexander.duyck@gmail.com>
Subject: Re: [PATCH net-next] mlx4: Better use of order-0 pages in RX path
Date: Mon, 13 Mar 2017 16:40:51 -0700	[thread overview]
Message-ID: <20170313234050.GA82263@ast-mbp.thefacebook.com> (raw)
In-Reply-To: <CANn89iL3ODh0xf=+P0gSYN-mGwACeeCO+OwtJzK5JEtOtMdPuw@mail.gmail.com>

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@gmail.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.