From: Tariq Toukan <tariqt@mellanox.com>
To: Jesper Dangaard Brouer <brouer@redhat.com>,
Jakub Kicinski <jakub.kicinski@netronome.com>
Cc: "David S. Miller" <davem@davemloft.net>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
Eran Ben Elisha <eranbe@mellanox.com>,
Alexander Duyck <alexander.duyck@gmail.com>
Subject: Re: [PATCH net-next 1/2] net: Take common prefetch code structure into a function
Date: Wed, 8 May 2019 07:48:00 +0000 [thread overview]
Message-ID: <bfc82029-8b74-26f5-35db-034cda3836ad@mellanox.com> (raw)
In-Reply-To: <20190507120857.5975c059@carbon>
On 5/7/2019 1:08 PM, Jesper Dangaard Brouer wrote:
> On Mon, 6 May 2019 16:51:57 -0700
> Jakub Kicinski <jakub.kicinski@netronome.com> wrote:
>
>> On Sun, 5 May 2019 13:36:06 +0300, Tariq Toukan wrote:
>>> Many device drivers use the same prefetch code structure to
>>> deal with small L1 cacheline size.
>>> Take this code into a function and call it from the drivers.
>>>
>>> Suggested-by: Jakub Kicinski <jakub.kicinski@netronome.com>
>>> Signed-off-by: Tariq Toukan <tariqt@mellanox.com>
>>> Reviewed-by: Saeed Mahameed <saeedm@mellanox.com>
>>> Cc: Jesper Dangaard Brouer <brouer@redhat.com>
>>
>> We could bike shed on the name a little - net_prefetch_headers() ?
>> but at least a short kdoc explanation for the purpose of this helper
>> would be good IMHO.
>
> I would at least improve the commit message. As Alexander so nicely
> explained[1], this prefetch purpose: "the 2 prefetches are needed for x86
> if you want a full TCP or IPv6 header pulled into the L1 cache for
> instance." Although, this is not true for a minimum TCP-packet
> Eth(14)+IP(20)+TCP(20)=54 bytes. An I missing an alignment in my calc?
>
> [1] https://lore.kernel.org/netdev/CAKgT0UeEL3W42eDqSt97xnn3tXDtWMf4sdPByAtvbx=Z7Sx7hQ@mail.gmail.com/
>
> The name net_prefetch_headers() suggested by Jakub makes sense, as this
> indicate that this should be used for prefetching packet headers.
>
> As Alexander also explained, I was wrong in thinking the HW DCU (Data
> Cache Unit) prefetcher will fetch two cache-lines automatically. As
> the DCU prefetcher is a streaming prefetcher, and doesn't see our
> access pattern, which is why we need this.
>
Thanks all for your comments.
I will fix and re-spin once the window re-opens.
Tariq
next prev parent reply other threads:[~2019-05-08 7:48 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-05 10:36 [PATCH net-next 0/2] Introduce net_prefetch Tariq Toukan
2019-05-05 10:36 ` [PATCH net-next 1/2] net: Take common prefetch code structure into a function Tariq Toukan
2019-05-06 23:51 ` Jakub Kicinski
2019-05-07 10:08 ` Jesper Dangaard Brouer
2019-05-08 7:48 ` Tariq Toukan [this message]
2019-05-05 10:36 ` [PATCH net-next 2/2] net/mlx5e: RX, Add a prefetch command for small L1_CACHE_BYTES Tariq Toukan
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