On Wed, Sep 23, 2020 at 10:00:41AM -0500, George Prekas wrote: > If an interrupt arrives between llist_add and > send_call_function_single_ipi in the following code snippet, then the > remote CPU will not receive the IPI in a timely manner and subsequent > SMP calls even from other CPUs for other functions will be delayed: > > if (llist_add(node, &per_cpu(call_single_queue, cpu))) > send_call_function_single_ipi(cpu); > > Note: llist_add returns 1 if it was empty before the operation. > > CPU 0 | CPU 1 | CPU 2 > __smp_call_single_q(2,f1) | __smp_call_single_q(2,f2) | > llist_add returns 1 | | > interrupted | llist_add returns 0 | > ... | branch not taken | > ... | | > resumed | | > send_call_function_single_ipi | | > | | f1 > | | f2 > > The call from CPU 1 for function f2 will be delayed because CPU 0 was > interrupted.
Do you happen to have any actual numbers and a use-case where this was relevant?
