PC Processors

[wurzlsepp]

Hi,

I wrote a small test program to see how long MWAITX sleeps in the case of write accesses to a monitored cache line.

I found that the instruction does not wake up at all when the write is not performed by a sibling thread.

In my opinion, this behavior contradicts what is stated in the AMD Architecture Programmer's Manual (Volume 3, it states that "A store from another processor matches the address range established by the MONITORX instruction" should cause a wakeup)

I saw this behavior on Zen2, Zen3, and Zen4c machines alike.

Changing the requested C-State does not influence this behavior at all.

I already contacted the customer support in this regard and was pointed to this forum here, hence the post.

Can anyone else confirm this behavior?

[elstaci]

Too technical for me to answer but maybe AMD SUPPORT might be able to explain from here: https://www.amd.com/en/forms/contact-us/support.html

[wurzlsepp]

Unfortunately, I already tried to reach out to them but was referred to this forum. Hence, I'm unsure as to whether I should contact them again.

I also think that this is not a question necessarily fit for the developer forum as it is either an issue with the specification of MWAITX or a bug in its implementation...