netdev - Re: [PATCH] mlx4_en: fix transmit of packages when blue frame is enabled

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Date:	Mon, 10 Oct 2011 11:24:05 +0200
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Eli Cohen <eli@....mellanox.co.il>
Cc:	David Laight <David.Laight@...LAB.COM>, netdev@...r.kernel.org,
	Eli Cohen <eli@...lanox.co.il>, linuxppc-dev@...ts.ozlabs.org,
	Thadeu Lima de Souza Cascardo <cascardo@...ux.vnet.ibm.com>,
	Yevgeny Petrilin <yevgenyp@...lanox.co.il>
Subject: Re: [PATCH] mlx4_en: fix transmit of packages when blue frame is
 enabled

On Mon, 2011-10-10 at 11:16 +0200, Eli Cohen wrote:

> Until then I think we need to have the logic working right on ppc and
> measure if blue flame buys us any improvement in ppc. If that's not
> the case (e.g because write combining is not working), then maybe we
> should avoid using blueflame in ppc.
> Could any of the guys from IBM check this and give us feedback?

I don't have the necessary hardware myself to test that but maybe Thadeu
can.

Note that for WC to work, things must be mapped non-guarded. You can do
that by using ioremap_prot() with pgprot_noncached_wc(PAGE_KERNEL) or
ioremap_wc() (dunno how "generic" the later is).

>From there, you should get write combining provided that you don't have
barriers between every access (ie those copy operations in their current
form should do the trick).

Cheers,
Ben.

> > Maybe it's time for us to revive those discussions about providing a
> > good set of relaxed MMIO accessors with explicit barriers :-)
> > 
> > Cheers,
> > Ben.
> >  


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