[lld] r232460 - [ELF] Use parallel_for_each for writing.

[Rafael Espíndola]

Attached is the full log of o new run.

On 19 March 2015 at 13:11, Shankar Easwaran <shankare at codeaurora.org> wrote:
> Hi Rafael,
>
> Thanks for the info.
>
> Any idea how many context switches that gold ends up with ?
>
> Shankar Easwaran
>
>
> On 3/19/2015 11:07 AM, Rafael Espíndola wrote:
>>
>> On 18 March 2015 at 20:26, Sean Silva <silvas at purdue.edu> wrote:
>>>
>>>
>>> On Wed, Mar 18, 2015 at 9:38 AM, Rui Ueyama <ruiu at google.com> wrote:
>>>>
>>>> It's not strange. Making something parallel doesn't always make it run
>>>> faster. Oftentimes it makes thing even slower. That's the whole point
>>>> why I
>>>> emphasized the importance of accurate benchmark. (Note that this is a
>>>> result
>>>> of linking Clang. You might see different results depending on
>>>> programs.)
>>>
>>>
>>> Actually I'm wondering if we're doing *anything* in parallel, since perf
>>> is
>>> reporting "0.999 CPUs utilized".
>>
>> Gah!
>>
>> I was wondering about that too and today it hit me: The "-a 0x4" in
>> the schedtool invocation was constraining the process to a particular
>> core. A leftover from benchmarking too many single threaded things :-(
>>
>> I ran the link again (in a fresh build, sorry). What I got was
>>
>> lld:
>> 2544.422504      task-clock (msec)         #    1.837 CPUs utilized
>>          ( +-  0.13%
>>   1.385020712 seconds time elapsed
>>      ( +-  0.15% )
>>
>> lld-revert
>>   2465.438485      task-clock (msec)         #    1.655 CPUs utilized
>>           ( +-  0.30% )
>> 1.489689761 seconds time elapsed
>>     ( +-  0.31% )
>>
>> gold:
>> 918.859273      task-clock (msec)         #    0.999 CPUs utilized
>>         ( +-  0.01% )
>> 0.919717669 seconds time elapsed
>>     ( +-  0.01% )
>>
>> gold --threads
>>   1300.210314      task-clock (msec)         #    1.523 CPUs utilized
>>           ( +-  0.15% )
>> 0.853835099 seconds time elapsed
>>     ( +-  0.25% )
>>
>>
>> So it looks like Shankar's patch does help.
>>
>> Really sorry about the noise. I will reply to the main "lld
>> performance" thread after lunch.
>>
>> Cheers,
>> Rafael
>>
>
>
> --
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by
> the Linux Foundation
>
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