On 06/23/2013 12:29 PM, Henrique de Moraes Holschuh wrote:
> On Sun, 23 Jun 2013, H. Peter Anvin wrote:
>> Why do you care about performance when PAT is disabled?
>
> It will regress already slow boxes. We blacklist a LOT of P4s, PMs, etc and
> nobody ever took the pain to track down which ones of those actually have
> PAT+MTRR aliasing bugs.
>
> These boxes have boards like the Radeon X300, which needs either PAT or MTRR
> to not become unusable...
>
We're talking hardware which is now many years old, but this is causing
very serious problems on real, modern hardware. As far as I understand
it, too, the blacklisting was precautionary (the only bug that I
personally know about is a performance bug, where WC would be
incorrectly converted to UC.)
We need a way forward here. If it is the only way I think we would have
to sacrifice the old machines, but perhaps something can be worked out
(e.g. if PAT is disabled, fall back to MTRRs if available for ioremap_wc()).
-hpa
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
