From: Mike Fedyk <mfedyk@matchmail.com>
To: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Jamie Lokier <lk@tantalophile.demon.co.uk>,
Dan Kegel <dank@kegel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Zach Brown <zab@zabbo.net>
Subject: Re: is CONFIG_PACKET_MMAP always a win?
Date: Fri, 22 Feb 2002 13:44:08 -0800 [thread overview]
Message-ID: <20020222214408.GI20060@matchmail.com> (raw)
In-Reply-To: <20020222190431.A16926@kushida.apsleyroad.org> <E16eLoz-0002vD-00@the-village.bc.nu>
In-Reply-To: <E16eLoz-0002vD-00@the-village.bc.nu>
On Fri, Feb 22, 2002 at 07:57:33PM +0000, Alan Cox wrote:
> > > You can process them in the ring buffer. If you can't keep up then you
> > > are screwed any way you look at it 8)
> >
> > That still doesn't avoid copying: af_packet copies the whole packet (if
> > you want the whole packet) from the original skbuff to the ring buffer.
>
> I'd make a handwaved claim that the first copy of the packet from a DMA
> receiving source is free. Its certainly pretty close to free because the
> overhead of sucking it into L1 cache will dominate and you need to do that
> anyway.
>
Doesn't DMA access system memory directly and leave processor caches alone?
If so, then the fewer copies that have to pollute the L1/2 caches the better.
Even if it does for UP, I'd immagine that it doesn't for SMP...
Mike
next prev parent reply other threads:[~2002-02-22 21:44 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-02-22 1:51 is CONFIG_PACKET_MMAP always a win? Dan Kegel
2002-02-22 2:33 ` Alan Cox
2002-02-22 5:59 ` David S. Miller
2002-02-22 6:45 ` Ben Greear
2002-02-22 8:37 ` Gianni Tedesco
2002-02-22 7:04 ` Dan Kegel
2002-02-22 14:04 ` Maciej W. Rozycki
2002-02-22 18:09 ` Jamie Lokier
2002-02-22 18:40 ` Alan Cox
2002-02-22 19:04 ` Jamie Lokier
2002-02-22 19:57 ` Alan Cox
2002-02-22 21:44 ` Mike Fedyk [this message]
2002-02-23 0:24 ` Alan Cox
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