> In the mips, mips64, and even the i386 arch, arch/kernel/smp.c has > this in smp_call_function: > > spin_lock(&call_lock); > call_data = &data; > > /* Send a message to all other CPUs and wait for them to respond */ > for (i = 0; i < smp_num_cpus; i++) > if (i != cpu) > core_send_ipi(i, SMP_CALL_FUNCTION); > > call_data isn't volatile, it's a plain static *. So how can we be sure > that "call_data = &data" does anything other than change a register? > > The i386 has a wb() after the assignment; we don't even have that. call_data is neither local nor static to the function, so the modification of the storage location would seem to be mandatory for the compiler before the call to core_send_ipi(), so I can see how the code, as written, would generally work on most MIPS CPUs. However, it would be legal for the compiler to defer the store until *just* before the invocation of core_send_ipi(), and on moderately complex, high-ILP processors it seems to me like the wb() might well be necessary. I take it that you've observed a problem with this on your system?:
