An introduction to lockless algorithms [LWN.net]

An introduction to lockless algorithms

Posted Feb 21, 2021 19:13 UTC (Sun) by khim (subscriber, #9252)
In reply to: An introduction to lockless algorithms by pbonzini
Parent article: An introduction to lockless algorithms

> On x86 that reordering cannot happen, on ARM and PowerPC it might.

Tiny correction: on x86 it can and will happen. You need memory barriers there, too.

After reading the aforementioned article I was confused for some time: memory barriers arrived on x86 with SSE… yet SMP was supported for more than decade by that time! Some investigation showed that any instruction with lock prefix acts as a memory barrier on x86. But if there are not memory barriers at all… yes, it does happen on x86, too.

An introduction to lockless algorithms

Posted Feb 21, 2021 20:51 UTC (Sun) by pbonzini (subscriber, #60935) [Link]

It can't happen until part 3. :) This article and the next one are only concerned with load-load and store-store reordering, which are not possible on x86.