Re: MTRR use in drivers

From: H. Peter Anvin
Date: Sun Jun 23 2013 - 10:08:28 EST

Why do you care about performance when PAT is disabled?

Brice Goglin <brice.goglin@xxxxxxxxx> wrote:

>Le 21/06/2013 07:00, H. Peter Anvin a Ãcrit :
>> An awful lot of drivers, mostly DRI drivers, are still mucking with
>> MTRRs directly as opposed to using ioremap_wc() or similar
>> In addition to the architecture dependency, this is really
>> because MTRRs are a limited resource, whereas page table attributes
>are not.
>> Furthermore, this perpetuates the need for the horrific hack known as
>> "MTRR cleanup".
>> What, if anything, can we do to clean up this mess?
>> -hpa
>The first network driver that used ioremap_wc() back in 2008 (myri10ge)
>had to keep using MTRR because ioremap_wc() silently falls back to
>ioremap_nocache() when PAT is disabled.
>I asked about this in and there was
>some talk about putting the MTRR addition in the nocache fallback path
>but I guess nobody implemented the idea.

Sent from my mobile phone. Please excuse brevity and lack of formatting.
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