From: tip tree robot <tip...@zytor.com> Sent: Tuesday, November 6, 2018 2:28 PM > > Committer: Thomas Gleixner <t...@linutronix.de> > CommitDate: Tue, 6 Nov 2018 23:20:13 +0100 > > 2) Managed interrupts: > > Managed interrupts guarantee vector reservation when the MSI/MSI-X > functionality of a device is enabled, which is achieved by reserving > vectors in the bitmaps of the possible target CPUs. This reservation > decrements the available count on each possible target CPU. >
Thomas, For the curious, could you elaborate on the reservation guarantee for managed interrupts? What exactly is guaranteed? I'm trying to understand the benefit of reserving a vector on all possible target CPUs. I can imagine this may be to related hot-remove of CPUs, but I'm not seeing the scenario where reserving on all possible target CPUs solves any fundamental problem. irq_build_affinity_masks() assigns spreads target CPUs across each IRQ in the batch, so you might get a small handful of possible target CPUs for each IRQ. But if those small handful of CPUs were to be hot-removed, then all the reserved vectors disappear anyway. So maybe there's another scenario I'm missing. Thanks, Michael
