Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20230525125746.553874-1-aleksander.lobakin@intel.com>
 <20230525125746.553874-4-aleksander.lobakin@intel.com> <8828262f1c238ab28be9ec87a7701acd791af926.camel@gmail.com>
 <cb7d3479-63a5-31b4-355d-b12a7e1b2878@intel.com> <CAKgT0Ud204CiJeB-5zcTKdrv7ODrfP09t73CqRhps7g3qhWU5w@mail.gmail.com>
 <d375fef9-43c4-9f2a-41c9-5247fcb3aa1e@intel.com> <CAKgT0Uc4UQ=PpVtjUAP=hjTDrWWkc79PeSwp39T6MSpo1ZyOag@mail.gmail.com>
 <cd88ac7e-fe82-fdc0-3410-0decf57d3c43@intel.com> <CAKgT0UeEz2Gqb62sn0pP3_yBMc-LpR0Twmv5_HTREvHBLpCsNw@mail.gmail.com>
 <5aac6822-6fe5-e182-935e-7aa86f1e820d@intel.com>
In-Reply-To: <5aac6822-6fe5-e182-935e-7aa86f1e820d@intel.com>
From:   Alexander Duyck <alexander.duyck@gmail.com>
Date:   Tue, 6 Jun 2023 07:24:47 -0700
Message-ID: <CAKgT0UegFu3LDhwx+ec8q1=c3OFzrKp=mhopzRFr84s4m9Ciug@mail.gmail.com>
Subject: Re: [Intel-wired-lan] [PATCH net-next v2 03/12] iavf: optimize Rx
 buffer allocation a bunch
To:     Alexander Lobakin <aleksander.lobakin@intel.com>
Cc:     Paul Menzel <pmenzel@molgen.mpg.de>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        Larysa Zaremba <larysa.zaremba@intel.com>,
        netdev@vger.kernel.org,
        Ilias Apalodimas <ilias.apalodimas@linaro.org>,
        linux-kernel@vger.kernel.org,
        "David S. Miller" <davem@davemloft.net>,
        Eric Dumazet <edumazet@google.com>,
        Michal Kubiak <michal.kubiak@intel.com>,
        intel-wired-lan@lists.osuosl.org, Jakub Kicinski <kuba@kernel.org>,
        Paolo Abeni <pabeni@redhat.com>,
        Christoph Hellwig <hch@lst.de>,
        Magnus Karlsson <magnus.karlsson@intel.com>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Precedence: bulk

On Tue, Jun 6, 2023 at 5:49=E2=80=AFAM Alexander Lobakin
<aleksander.lobakin@intel.com> wrote:
>
> From: Alexander Duyck <alexander.duyck@gmail.com>
> Date: Fri, 2 Jun 2023 10:50:02 -0700
>
> Sorry for the silence, had sorta long weekend :p
>
> > On Fri, Jun 2, 2023 at 9:16=E2=80=AFAM Alexander Lobakin
> > <aleksander.lobakin@intel.com> wrote:
>

[...]

> > The other thing is you may want to double check CPU(s) you are
> > expected to support as last I knew switch statements were still
> > expensive due to all the old spectre/meltdown workarounds.
> Wait, are switch-cases also affected? I wasn't aware of that. For sure I
> didn't even consider using ops/indirect calls, but switch-cases... I saw
> lots o'times people replacing indirections with switch-cases, what's the
> point otherwise :D
>
> Thanks,
> Olek

I think it all depends on how the compiler implements them. I know
switch cases used to be done as indirections in some cases. It is
possible they did away with that in the compilers some time ago or
came up with a fix to work around them. I just remember back when that
came up people were going through and replacing switch cases with
if/else blocks in the case of performance sensitive workloads. Odds
are there have been workarounds added to address that, but it is just
something to be aware of.

Thanks,

- Alex