[RFC] implement QUEUED spinlocks on powerpc

[Eric Dumazet]

On Wed, Feb 1, 2017 at 8:04 PM, Michael Ellerman <mpe at ellerman.id.au> wrote:
> Benjamin Herrenschmidt <benh at kernel.crashing.org> writes:
>
>> On Wed, 2017-02-01 at 09:05 -0800, Eric Dumazet wrote:
>>> Hi all
>>>
>>> Is anybody working on adding QUEUED spinlocks to powerpc 64bit ?
>>>
>>> I've seen past attempts with ticket spinlocks
>>> ( https://patchwork.ozlabs.org/patch/449381/ and other related links
>>> )
>>>
>>> But it looks ticket spinlocks are a thing of the past.
>>
>> Yes, we have a tentative implementation of qspinlock and pv variants:
>>
>> https://patchwork.ozlabs.org/patch/703139/
>> https://patchwork.ozlabs.org/patch/703140/
>> https://patchwork.ozlabs.org/patch/703141/
>> https://patchwork.ozlabs.org/patch/703142/
>> https://patchwork.ozlabs.org/patch/703143/
>> https://patchwork.ozlabs.org/patch/703144/
>>
>> Michael, what's the status with getting that merged ?
>
> Needs a good review, and the benchmark results were not all that
> compelling - though perhaps they were just the wrong benchmarks.

A typical benchmark would be to use 200 concurrent netperf -t TCP_RR,
through a single qdisc (protected by a spinlock)

Non ticket/queued spinlocks behave quite bad in this scenario.

I can try this next week if you want.