[dpdk-dev] [RFC 1/6] eal: add power management intrinsics

[Burakov, Anatoly]

On 28-May-20 12:39 PM, Ananyev, Konstantin wrote:
> Hi Anatoly,
> 
>>
>> Add two new power management intrinsics, and provide an implementation
>> in eal/x86 based on UMONITOR/UMWAIT instructions. The instructions
>> are implemented as raw byte opcodes because there is not yet widespread
>> compiler support for these instructions.
>>
>> The power management instructions provide an architecture-specific
>> function to either wait until a specified TSC timestamp is reached, or
>> optionally wait until either a TSC timestamp is reached or a memory
>> location is written to. The monitor function also provides an optional
>> comparison, to avoid sleeping when the expected write has already
>> happened, and no more writes are expected.
> 
> Recently ARM guys introduced new generic API
> for similar (as I understand) purposes: rte_wait_until_equal_(16|32|64).
> Probably would make sense to unite both APIs into something common
> and HW transparent.
> Konstantin

Hi Konstantin,

That's not really similar purpose. This is monitoring a cacheline for 
writes, not waiting on a specific value. The "expected" value is there 
as basically a hack to get around the race condition due to the fact 
that by the time you enter monitoring state, the write you're waiting 
for may have already happened.

-- 
Thanks,
Anatoly