Re: RFC: x86-64: Use fxsave/xsave/xsavec in _dl_runtime_resolve [BZ #21265]

[Carlos O'Donell <carlos at redhat dot com>]

On 10/20/2017 09:31 AM, Florian Weimer wrote:
> * Florian Weimer:
> 
>> On 10/20/2017 03:21 PM, Florian Weimer wrote:
>>> LD_DEBUG=statistics shows this:
>>>
>>>        9506:
>>>        9506:     runtime linker statistics:
>>>        9506:       total startup time in dynamic loader: 19960074 cycles
>>>        9506:                 time needed for relocation: 19105814 cycles 
>>> (95.7%)
>>>        9506:                      number of relocations: 87
>>>        9506:           number of relocations from cache: 3
>>>        9506:             number of relative relocations: 1226
>>>        9506:                time needed to load objects: 701382 cycles 
>>> (3.5%)
>>>        9506:
>>>        9506:     runtime linker statistics:
>>>        9506:                final number of relocations: 781589
>>>        9506:     final number of relocations from cache: 3
>>>
>>> This is a main program which contains 1,500 function calls.  The 
>>> functions are defined in a single DSO, and each function calls 520 other 
>>> functions, giving a total number of 781,500 relocations from the test.
>>>
>>> On my laptop (Intel(R) Core(TM) i7-4810MQ CPU @ 2.80GHz), I get this 
>>> (ten runs, real time measured in seconds):
>>>
>>>  > t.test(prev_laptop, after_laptop)
>>>
>>>      Welch Two Sample t-test
>>>
>>> data:  prev_laptop and after_laptop
>>> t = -14.932, df = 18, p-value = 1.392e-11
>>> alternative hypothesis: true difference in means is not equal to 0
>>> 95 percent confidence interval:
>>>   -0.05749145 -0.04330855
>>> sample estimates:
>>> mean of x mean of y
>>>     0.2345    0.2849
>>>
>>> So it's definitely not in the noise.  The penalty appears to be around 
>>> 65ns per relocation.
>>
>> I did some more benchmarks.  Ryzen takes a bit of a hit (100ns or ~30%). 
>>   Purley looks very good (35ns or ~5%).  The outlier is KNL, with 750ns 
>> added per relocation (at lower clock rates admittedly) and ~50% longer 
>> relocation times overall.  (The caveat is that this is lab hardware, 
>> which may or may not match production silicon.)
> 
> I found another piece of perhaps interesting hardware, an Intel(R)
> Core(TM) m7-6Y75.  The performance hit is around 3% or 16ns.  This is
> a lower-power mobile CPU in a tablet.  So even there, the numbers are
> good.
 
Florian, H.J, and Markus,

Thank you very much for doing some more thourough tests on the patch set.

-- 
Cheers,
Carlos.