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Date: Thu, 24 Sep 2015 15:14:23 -0500 From: Scott Wood <scottwood@...escale.com> To: David Laight <David.Laight@...LAB.COM> CC: 'Christophe Leroy' <christophe.leroy@....fr>, Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, "Michael Ellerman" <mpe@...erman.id.au>, "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2 08/25] powerpc/8xx: Map IMMR area with 512k page at a fixed address On Thu, 2015-09-24 at 11:41 +0000, David Laight wrote: > From: Christophe Leroy > > Sent: 22 September 2015 17:51 > ... > > Traditionaly, each driver manages one computer board which has its > > own components with its own memory maps. > > But on embedded chips like the MPC8xx, the SOC has all registers > > located in the same IO area. > > > > When looking at ioremaps done during startup, we see that > > many drivers are re-mapping small parts of the IMMR for their own use > > and all those small pieces gets their own 4k page, amplifying the > > number of TLB misses: in our system we get 0xff000000 mapped 31 times > > and 0xff003000 mapped 9 times. > > Isn't this a more general problem? > > If there are multiple remap requests for the same physical page > shouldn't the kernel be just increasing a reference count somewhere > and returning address in the same virtual page? > This should probably happen regardless of the address. > I presume it must be done for cacheable mappings. Why would you assume that? -Scott -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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