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From: Alexander Duyck <alexander.duyck@gmail.com>
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>
Subject: Re: [Intel-wired-lan] [PATCH net-next v2 03/12] iavf: optimize Rx buffer allocation a bunch
Date: Tue, 6 Jun 2023 07:24:47 -0700	[thread overview]
Message-ID: <CAKgT0UegFu3LDhwx+ec8q1=c3OFzrKp=mhopzRFr84s4m9Ciug@mail.gmail.com> (raw)
In-Reply-To: <5aac6822-6fe5-e182-935e-7aa86f1e820d@intel.com>

On Tue, Jun 6, 2023 at 5:49 AM 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 AM 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

WARNING: multiple messages have this Message-ID (diff)
From: Alexander Duyck <alexander.duyck@gmail.com>
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, Christoph Hellwig <hch@lst.de>,
	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>,
	"David S. Miller" <davem@davemloft.net>,
	Magnus Karlsson <magnus.karlsson@intel.com>
Subject: Re: [Intel-wired-lan] [PATCH net-next v2 03/12] iavf: optimize Rx buffer allocation a bunch
Date: Tue, 6 Jun 2023 07:24:47 -0700	[thread overview]
Message-ID: <CAKgT0UegFu3LDhwx+ec8q1=c3OFzrKp=mhopzRFr84s4m9Ciug@mail.gmail.com> (raw)
In-Reply-To: <5aac6822-6fe5-e182-935e-7aa86f1e820d@intel.com>

On Tue, Jun 6, 2023 at 5:49 AM 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 AM 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
_______________________________________________
Intel-wired-lan mailing list
Intel-wired-lan@osuosl.org
https://lists.osuosl.org/mailman/listinfo/intel-wired-lan

  reply	other threads:[~2023-06-06 14:26 UTC|newest]

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-05-25 12:57 [Intel-wired-lan] [PATCH net-next v2 00/12] net: intel: start The Great Code Dedup + Page Pool for iavf Alexander Lobakin
2023-05-25 12:57 ` Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 01/12] net: intel: introduce Intel Ethernet common library Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 02/12] iavf: kill "legacy-rx" for good Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-30 15:29   ` Alexander H Duyck
2023-05-30 15:29     ` [Intel-wired-lan] " Alexander H Duyck
2023-05-30 16:22     ` Alexander Lobakin
2023-05-30 16:22       ` [Intel-wired-lan] " Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 03/12] iavf: optimize Rx buffer allocation a bunch Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-30 16:18   ` Alexander H Duyck
2023-05-30 16:18     ` [Intel-wired-lan] " Alexander H Duyck
2023-05-31 11:14     ` Maciej Fijalkowski
2023-05-31 11:14       ` [Intel-wired-lan] " Maciej Fijalkowski
2023-05-31 15:22       ` Alexander Lobakin
2023-05-31 15:22         ` [Intel-wired-lan] " Alexander Lobakin
2023-05-31 15:13     ` Alexander Lobakin
2023-05-31 15:13       ` Alexander Lobakin
2023-05-31 17:22       ` Alexander Duyck
2023-06-02 13:58         ` Alexander Lobakin
2023-06-02 13:58           ` Alexander Lobakin
2023-06-02 15:04           ` Alexander Duyck
2023-06-02 15:04             ` Alexander Duyck
2023-06-02 16:15             ` Alexander Lobakin
2023-06-02 16:15               ` Alexander Lobakin
2023-06-02 17:50               ` Alexander Duyck
2023-06-02 17:50                 ` Alexander Duyck
2023-06-06 12:47                 ` Alexander Lobakin
2023-06-06 12:47                   ` Alexander Lobakin
2023-06-06 14:24                   ` Alexander Duyck [this message]
2023-06-06 14:24                     ` Alexander Duyck
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 04/12] iavf: remove page splitting/recycling Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 05/12] iavf: always use a full order-0 page Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-26  8:57   ` David Laight
2023-05-26  8:57     ` [Intel-wired-lan] " David Laight
2023-05-26 12:52     ` Alexander Lobakin
2023-05-26 12:52       ` [Intel-wired-lan] " Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 06/12] net: skbuff: don't include <net/page_pool.h> into <linux/skbuff.h> Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-27  3:54   ` Jakub Kicinski
2023-05-27  3:54     ` [Intel-wired-lan] " Jakub Kicinski
2023-05-30 13:12     ` Alexander Lobakin
2023-05-30 13:12       ` [Intel-wired-lan] " Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 07/12] net: page_pool: avoid calling no-op externals when possible Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 08/12] net: page_pool: add DMA-sync-for-CPU inline helpers Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 09/12] iavf: switch to Page Pool Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 10/12] libie: add common queue stats Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 11/12] libie: add per-queue Page Pool stats Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin
2023-05-25 12:57 ` [Intel-wired-lan] [PATCH net-next v2 12/12] iavf: switch queue stats to libie Alexander Lobakin
2023-05-25 12:57   ` Alexander Lobakin

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