netdev - Re: [PATCH net-next] net: add a prefetch in socket backlog processing

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Message-ID: <1335875351.11396.55.camel@edumazet-glaptop>
Date:	Tue, 01 May 2012 14:29:11 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Joe Perches <joe@...ches.com>
Cc:	David Miller <davem@...emloft.net>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next] net: add a prefetch in socket backlog
 processing

On Tue, 2012-05-01 at 04:52 -0700, Joe Perches wrote:

> That's true for cpus with sufficient cache but prefetch
> might be wasteful for cpus without (like some ARMs).
> 

> Some of the sk_backlog_rcv functions like tcp_v4_do_rcv
> can be relatively large.

You speak of icache here. Thats different matter.

My patch does a prefetch of data (dcache)

> 
> It might be useful to have a target cpu compile time
> test precede this prefetch.

How this prefetch() is different than other ones in kernel ?

We optimize linux for cpus with a minimum cache, not for the ones with
less than 16KB caches.

For old cpus, you can use linux 2.4 it works much better.

If you believe there is an issue on a particular arch, I suggest you
talk with arch maintainer about ARCH_HAS_PREFETCH being undefined on
this arch.

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