RFC: x86: Enable -z separate-code by default

H.J. Lu hjl.tools@gmail.com
Thu Feb 22 17:43:00 GMT 2018


On Thu, Feb 22, 2018 at 6:25 AM, H.J. Lu <hjl.tools@gmail.com> wrote:
> On Thu, Feb 22, 2018 at 5:22 AM, Michael Matz <matz@suse.de> wrote:
>> Hi,
>>
>> 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.
>

Here is the patch which sets maximum page size to 2MB page size when
-z separate-code is disabled by default.


-- 
H.J.
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