On Wed, 26 Aug 2015, Qais Yousef wrote: > On 08/26/2015 02:19 PM, Thomas Gleixner wrote: > > Wrong. You cannot move an IPI around with set_affinity. It's possible > > to send an IPI to more than one target CPU, but that has nothing to do > > with affinities. > > > > Are you talking about IPIs or about general interrupts which have an > > affinity setting? > > Maybe my view of the world is limited. I wrote this because the mechanism to > route an IPI and set affinities is the same. That might be the case on your particular platform, but that's not generally true. > So specifying which core or hardware thread should Linux CPU route this IPI to > is the same as setting the affinity, no? Linux will not move the IPI that is > routed to the coprocessor core. Just the IPI it will receive. > > Also the way I see it is that this is an external interrupt whether it was > asserted by real signal or through IPI mechanism and it should be treated as > such in terms of moving inside Linux SMP, no? Again maybe my view of the world > is limited but I can't see why migrating the interrupt would affect > correctness unless there's a hardware limitation like only core 0 can read > info from AXD (which is where my suggestion to using affinity hint above to > accommodate such limitations). > > When you say 'It is possible to send an IPI to more than one target CPU', is > it a case we need to cater for? The way I was seeing this problem is > communication between single Linux SMP and a single coprocessor unit. I didn't > think of it as single to many. Even if the coprocessor is a cluster I'd expect > it to act as a single unit like Linux SMP. And if it wanted to send 2 > different interrupts it will need to use 2 different IPIs. You are confusing the terms. IPI = Inter Processor Interrupt As the name says that's an interrupt which goes from one cpu to another. So an IPI has a very clear target. Whether the platform implements IPIs via general interrupts which are made affine to a particular cpu or some other specialized mechanism is completely irrelevant. An IPI is not subject to affinity settings, period. So if you want to use an IPI then you need a target cpu for that IPI. If you want something which can be affined to any cpu, then you need a general interrupt and not an IPI. That's what I asked before and you still did not answer that question. > > Are you talking about IPIs or about general interrupts which have an > > affinity setting? Thanks, tglx
