[PATCH] powerpc/rtas: retry when cpu offline races with suspend/migration

[Juliet Kim]

There's some concern this could retry forever, resulting in live lock.  
Another approach would be to abandon the attempt and fail the LPM 
request. 
https://lists.ozlabs.org/pipermail/linuxppc-dev/2019-June/192531.html

On 6/24/19 12:23 PM, Nathan Lynch wrote:
> Hi Mingming,
>
> mmc <mmc at linux.vnet.ibm.com> writes:
>> On 2019-06-21 00:05, Nathan Lynch wrote:
>>> So return -EAGAIN instead of -EBUSY when this race is
>>> encountered. Additionally: logging this event is still appropriate but
>>> use pr_info instead of pr_err; and remove use of unlikely() while here
>>> as this is not a hot path at all.
>> Looks good, since it's not a hot path anyway, so unlikely() should
>> benefit from optimize compiler path, and should stay. No?
> The latency of this path in rtas_ibm_suspend_me() in the best case is
> around 2-3 seconds.
>
> So I think not -- this is such a heavyweight and relatively
> seldom-executed path that the unlikely() cannot yield any discernible
> performance benefit, and its presence imposes a readability cost.