From: David Miller <davem@davemloft.net>
To: alexander.h.duyck@intel.com
Cc: eric.dumazet@gmail.com, jeffrey.t.kirsher@intel.com,
mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com,
x86@kernel.org, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, gospo@redhat.com
Subject: Re: [net-next-2.6 PATCH 2/2] x86: Align skb w/ start of cache line on newer core 2/Xeon Arch
Date: Thu, 10 Jun 2010 22:20:06 -0700 (PDT) [thread overview]
Message-ID: <20100610.222006.242136751.davem@davemloft.net> (raw)
In-Reply-To: <80769D7B14936844A23C0C43D9FBCF0F2562CD2555@orsmsx501.amr.corp.intel.com>
From: "Duyck, Alexander H" <alexander.h.duyck@intel.com>
Date: Wed, 2 Jun 2010 16:55:16 -0700
> Eric Dumazet wrote:
>>
>> But... L1_CACHE_BYTES is 64 on MCORE2, so this matches current
>> NET_SKB_PAD definition...
>>
>> #ifndef NET_SKB_PAD
>> #define NET_SKB_PAD 64
>> #endif
>
> I admit the current definition is redundant, but NET_SKB_PAD had
> been 32 until your recent change of the value, and prior to 2.6.30
> the value was 16. If the value were to change again it would
> silently break the cacheline alignment which is provided by this
> patch. If we were to define NET_SKB_PAD using L1_CACHE_BYTES in
> skbuff.h then I might be more inclined to to pull the NET_SKB_PAD
> change, but right now I would prefer to treat NET_SKB_PAD as a magic
> number that coincidently is the same size as the L1 cache on MCORE2.
Eric, why don't we do that? Make NET_SKB_PAD's define L1_CACHE_BYTES.
Reading the comments you added when the default value was changed to
64, this seems to even be your overall intent. :-)
next prev parent reply other threads:[~2010-06-11 5:19 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-02 22:24 [net-next-2.6 PATCH 1/2] skbuff: add check for non-linear to warn_if_lro and needs_linearize Jeff Kirsher
2010-06-02 22:25 ` [net-next-2.6 PATCH 2/2] x86: Align skb w/ start of cache line on newer core 2/Xeon Arch Jeff Kirsher
2010-06-02 22:44 ` Eric Dumazet
2010-06-02 23:55 ` Duyck, Alexander H
2010-06-02 23:55 ` Duyck, Alexander H
2010-06-11 5:20 ` David Miller [this message]
2010-06-14 12:57 ` [PATCH net-next-2.6] net: NET_SKB_PAD should depend on L1_CACHE_BYTES Eric Dumazet
2010-06-16 1:16 ` David Miller
2010-06-05 9:54 ` [net-next-2.6 PATCH 1/2] skbuff: add check for non-linear to warn_if_lro and needs_linearize David Miller
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