[aarch64-port-dev ] RFR: 8079203: aarch64: need to cater for different partner implementations
edward.nevill at linaro.org
Tue May 5 14:23:41 UTC 2015
On Fri, 2015-05-01 at 15:23 +0100, Mark Rutland wrote:
> From a look at the proposed patch, I guess this assumes a uniform SMP
> system (i.e. no big.LITTLE)?
Not quite: The assumption is that any CPU implementer == ARM could be big little and therefore could contain A53 and therefor the A53 feature must be enabled.
> A while back  the /proc/cpuinfo format was fixed to show information per-cpu
> (example form a Juno system below), and it looks like the CPU information
> parsed will only refer to ther final CPU listed, and may not be representative
> of the system as a whole.
> That format has been packported to the various stable kernels too.
Nonetheless, we must still cater for olde style /proc/cpuinfo. I have modified the webrev below so that if it is a new style /proc/cpuinfo, it will only enable the A53 feature if it can positively identify an A53 core.
Otherwise, if it is an old style /proc/cpuinfo it will assume the A53 feature needs enabling if it finds an A57 (or, of course if it is identified as an A53).
You're welcome. It would be much easier if the kernel exported this information in a machine readable form. I hate having to grub around in /proc/cpuinfo to find this information, and I know that others in the OpenJDK community hate this also. Its fragile and non portable.
Why can the kernel not make MIDR readable at EL0 and provide a HWCAP_BIGLITTLE in auxv.
All the best,
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