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Re: RFC: x86: Enable -z separate-code by default
On Thu, Feb 22, 2018 at 5:22 AM, Michael Matz <email@example.com> wrote:
> On Thu, 22 Feb 2018, H.J. Lu wrote:
>> >> Meh :-( Have you done any performance measurements on, say, SPECcpu?
>> > We will.
>> We compared SPEC CPU 2017 performance before and after this change on
>> Skylake server. There are no any significant performance changes.
>> Everything is mostly below +/-1%.
> Thanks, seems fine.
>> >>> Should I add an ld configure option, --enable-separate-code, instead?
>> >> Yes, definitely. For old distros at least I definitely want to retain old
>> >> behaviour by default and a configure switch would make that easier.
>> > Will do.
>> Here is the patch to add --enable-separate-code to ld configure and
>> enable it by default for Linux/x86. But the default maximum page size
>> is changed to 4KB for x86-64.
>> Any comments?
> Should the max page size setting (without override on cmdline) depend on
> separate-code, or not? I'm split minds here, I'm worried that the 2mb
I will give it a try.
> page size optimization we had for x86-64 isn't effective by default, but
> OTOH it already isn't since relro, so can't be that bad either, plus the
> kernel is of course free to use 2mb TLB entries when in the end the
> moons^Waddresses happen to be aligned right.
Gold defaults to 4KB page for x86-64.