linux-kernel - Re: [PATCH] X86: MM: Add PAT Type write-through in combination with mtrr

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Date:	Sun, 27 Oct 2013 20:01:48 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Andreas Werner <wernerandy@....de>
Cc:	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	x86@...nel.org, dave@...ux.vnet.ibm.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] X86: MM: Add PAT Type write-through in combination with
 mtrr

On Sun, Oct 27, 2013 at 06:56:08PM +0100, Andreas Werner wrote:
> Transmit Buffers WC (only write to that buffer)
> i have PICe bursts on my tracer.

For that you can do ioremap_wc().

> Receive Buffers WT (only read to that buffer). I use
> clflush_cache_range before reading from that adresses and i have PCIe
> bursts on my tracer.

That one I don't understand - why would you need a WT buffer? It only
caches reads but you will read from it only once after it has been
received. Why pollute the cache?

IOW, you probably could use a WC buffer here too, as it would combine
the writes coming from the FPGA.

Btw, there's also mtrr_add(..., MTRR_TYPE_WRTHROUGH, ) if you must use a
WT thing. Have you tried that?

> With UC memory there are no PCIe bursts and my bandwidth is very slow.

Right.

-- 
Regards/Gruss,
    Boris.

Sent from a fat crate under my desk. Formatting is fine.
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