[PATCH RFCv2 1/5] ARM: use write allocate by default on ARMv6+

Thomas Petazzoni thomas.petazzoni at free-electrons.com
Fri Jun 13 04:34:37 PDT 2014


On Fri, 13 Jun 2014 11:20:19 +0100, Russell King - ARM Linux wrote:

> > I spoke briefly about this with Albin Tonnerre from ARM, and his
> > feedback is that it should not cause any problem to set the SMP bit and
> > the shareable attribute even on non-SMP Cortex-A9 processors such as
> > the Aegis. If that's correct, then we could do it for all Cortex-A9,
> > without having to know whether what we have is a SoC from Marvell with
> > I/O coherency or any other Cortex-A9 based SoC.
> Setting the sharable attribute is not really a good idea - implementations
> are permitted to treat a writeback sharable mapping as uncacheable, which
> would be a severe performance degredation to single core CPUs.

Then maybe we could set the shareable attribute on SMP-capable
processors even if CONFIG_SMP is disabled? This way, those single core
CPUs that are really not SMP capable continue to run without the
shareable attribute, while all SMP-capable processors run with the
shareable attribute, regardless of whether the kernel is configured
CONFIG_SMP or not.

> The patches I sent during this thread are now merged into mainline.  The
> setting of the shared bit, and the memory cache policy are now both
> derived from the proc_info structures, specifically the __cpu_mm_mmu_flags
> member.

Right. So for Armada 370/XP, I'll update the proc_info structure. We
still have to find the right solution/compromise for the Armada 375/38x


Thomas Petazzoni, CTO, Free Electrons
Embedded Linux, Kernel and Android engineering

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