Re: [PATCH/AARCH64] Improved -mcpu/mtune/march=native handling

[Andreas Tobler <andreast-list at fgznet dot ch>]

On 11.11.16 11:06, Richard Earnshaw wrote:
> On 11/11/16 02:56, Andrew Pinski wrote:
> > As I mentioned in my other emails, parsing /proc/cpuinfo has one issue
> > is that the current parsing assumes many different things about the
> > format.  So the best way to do this is to parse
> > /sys/devices/system/cpu/cpuN/regs/identification/midr_el1 files
> > instead.  To get which cpu are present (though not necessarily online)
> > we parse "/sys/devices/system/cpu/present" file.  We fall back to
> > parsing /proc/cpu if any parsing fails of these files including not
> > finding out which cpu we are on.  The main reason why we fall back is
> > because only newer kernels support exporting this file.  To get the
> > features I just look at the hwcap that the kernel passes to userspace
> > so I needed to add an extra argument to AARCH64_OPT_EXTENSION.  I also
> > had to define some HWCAP_* macros in driver-aarch64.c since older
> > kernels headers don't have these values defined.
> >
> > It should also be possible to parse
> > /sys/devices/system/cpu/cpu%d/cache%d directory to get cache
> > information too but that is left for another patch and another time.
> >
> > Since I don't have access to a big.LITTLE system, someone should test
> > there with a new enough kernel; I was using stock 4.9.0-rc3.
> >
> > OK?  Bootstrapped and tested on ThunderX on aarch64-linux-gnu with no
> > regressions and making sure /proc/cpuinfo is not read (by using
> > strace).
> >
> > Thanks,
> > Andrew Pinski
> >
> > ChangeLog:
> > * config/aarch64/aarch64-option-extensions.def: Document extra
> > argument to AARCH64_OPT_EXTENSION.  Update for the extra argument for
> > all of the option extensions.
> > * config/aarch64/driver-aarch64.c: Include sys/auxv.h and asm/hwcap.h.
>
> GCC supports native builds on freebsd as well as linux.  Isn't this
> going to break that?

It will.
Andreas

> R.
>
> > (HWCAP_CRC32): Define if needed.
> > (HWCAP_ATOMICS): Likewise.
> > (HWCAP_FPHP): Likewise.
> > (HWCAP_ASIMDHP): Likewise.
> > (aarch64_arch_extension): New field hwcap_mask.
> > (AARCH64_OPT_EXTENSION): Handle extra argument.
> > (AARCH64_BIG_LITTLE): Always put the larger core number first.
> > (valid_bL_core_p): Don't check AARCH64_BIG_LITTLE for the opposite
> > order as it already handles the order.
> > (implementor_from_midr): New function.
> > (part_no_from_midr): New function.
> > (sysfsformat): New define.
> > (host_detect_local_cpu_sys): New function.
> > (host_detect_local_cpu): Call host_detect_local_cpu_sys if opening
> > "/sys/devices/system/cpu/present" file worked.
> > * common/config/aarch64/aarch64-common.c (AARCH64_OPT_EXTENSION):
> > Handle extra argument.