Re: [PATCH] X86-64: Add _dl_runtime_resolve_avx[512]_opt [BZ #20508]

["H.J. Lu" <hjl dot tools at gmail dot com>]

On Tue, Oct 4, 2016 at 2:18 PM, Adhemerval Zanella
<adhemerval.zanella@linaro.org> wrote:
>
>
> On 04/10/2016 18:00, H.J. Lu wrote:
>> On Tue, Oct 4, 2016 at 11:13 AM, Adhemerval Zanella
>> <adhemerval.zanella@linaro.org> wrote:
>>>
>>>
>>> On 04/10/2016 13:08, H.J. Lu wrote:
>>>> On Tue, Oct 4, 2016 at 8:48 AM, Florian Weimer <fweimer@redhat.com> wrote:
>>>>> On 10/04/2016 05:34 PM, H.J. Lu wrote:
>>>>>>
>>>>>> On Tue, Oct 4, 2016 at 8:24 AM, Florian Weimer <fweimer@redhat.com> wrote:
>>>>>>>
>>>>>>> On 10/04/2016 04:47 PM, H.J. Lu wrote:
>>>>>>>>
>>>>>>>>
>>>>>>>> On Tue, Oct 4, 2016 at 3:52 AM, Florian Weimer <fweimer@redhat.com>
>>>>>>>> wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 09/27/2016 07:35 PM, H.J. Lu wrote:
>>>>>>>>>
>>>>>>>>>>> Any comments? I will check it in next week if there is no objection.
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> I'd like to backport it to 2.23 and 2.24 branches.  Any objections?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Just this change, or the requirement for an AVX512F-capable assembler
>>>>>>>>> as
>>>>>>>>> well?
>>>>>>>>>
>>>>>>>>
>>>>>>>> Good question.  This is also needed:
>>>>>>>>
>>>>>>>> commit f43cb35c9b3c35addc6dc0f1427caf51786ca1d2
>>>>>>>> Author: H.J. Lu <hjl.tools@gmail.com>
>>>>>>>> Date:   Fri Jul 1 05:54:43 2016 -0700
>>>>>>>>
>>>>>>>>     Require binutils 2.24 to build x86-64 glibc [BZ #20139]
>>>>>
>>>>>
>>>>>>> That's not really backportable, I'm afraid.  Our users don't expect we
>>>>>>> break
>>>>>>> builds in this way.
>>>>>>>
>>>>>>
>>>>>> Who are those users?
>>>>>
>>>>>
>>>>> We don't know, really.  But moving forward the baseline binutils requirement
>>>>> in a stable release really contradicts what a stable release is about.
>>>>>
>>>>>
>>>>
>>>> Do our users expect a broken glibc binary of a stable release on AVX512
>>>> machine?
>>>>
>>>
>>> I think 2.24 it is ok since it contains the BZ#20139 fix already.  For 2.23,
>>> although it was not really explicit in NEWS, AVX512 is suppose to be supported
>>> in a set of different implementation (memmove/memcpy/libmvec).  However my
>>> understanding of this issue is limited to be a performance one, so I do not
>>> see a pressing matter to change a release requirements for such change.
>>
>> It is a regression from glibc 2.22.
>
> Right, but it is functional regression that prevent avx512 binaries to run
> correctly on glibc 2.23+ or a performance regression?

BZ #20508 is a performance regression.

-- 
H.J.