netdev - Re: [PATCH net-next] net: Implement fast csum_partial for x86

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Date:	Mon, 04 Jan 2016 15:52:56 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Tom Herbert <tom@...bertland.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Kernel Team <kernel-team@...com>
Subject: Re: [PATCH net-next] net: Implement fast csum_partial for x86_64

On Mon, 2016-01-04 at 15:34 -0800, Tom Herbert wrote:
> On Mon, Jan 4, 2016 at 2:36 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> > On Sun, 2016-01-03 at 15:22 -0800, Tom Herbert wrote:
> > \...
> >> +402: /* Length 2, align is 1, 3, or 5 */
> >> +     movb    (%rdi), %al
> >> +     movb    1(%rdi), %ah
> >
> > Looks like a movw (%rdi),%ax
> >
> Wouldn't that be an unaligned access?

x86 does not care. (This is why we have
CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)

I bet it is faster using a single instruction.



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