From: "David S. Miller" <davem@davemloft.net>
To: rdunlap@xenotime.net
Cc: borntrae@de.ibm.com, netdev@vger.kernel.org
Subject: Re: [RFC] changing value of NETDEV_ALIGN to cacheline size
Date: Mon, 15 May 2006 14:30:11 -0700 (PDT) [thread overview]
Message-ID: <20060515.143011.36635008.davem@davemloft.net> (raw)
In-Reply-To: <20060515080258.bdcfba5f.rdunlap@xenotime.net>
From: "Randy.Dunlap" <rdunlap@xenotime.net>
Date: Mon, 15 May 2006 08:02:58 -0700
> > -#define NETDEV_ALIGN 32
> > +#define NETDEV_ALIGN L1_CACHE_BYTES
> > #define NETDEV_ALIGN_CONST (NETDEV_ALIGN - 1)
>
> I don't know about the fixed value of 32, but if this patch is
> accepted, I'd prefer NETDEV_ALIGN_MASK instead of NETDEV_ALIGN_CONST.
The reason it's 32 is that old drivers depended on the
struct being at least 32-byte aligned because they would
embed structures DMA'd to/from the card in their private
area and just assumed that would be aligned enough for
the card's restrictions.
So setting it to L1_CACHE_BYTES would be wrong, because if
that happens to be less than 32 it would violate said
assumption which we are catering to.
next prev parent reply other threads:[~2006-05-15 21:30 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-05-15 12:08 [RFC] changing value of NETDEV_ALIGN to cacheline size Christian Borntraeger
2006-05-15 15:02 ` Randy.Dunlap
2006-05-15 21:30 ` David S. Miller [this message]
2006-05-15 21:39 ` Rick Jones
2006-05-15 21:58 ` Stephen Hemminger
2006-05-15 22:49 ` David S. Miller
2006-05-15 23:01 ` Rick Jones
2006-05-16 15:16 ` Christian Borntraeger
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