On Fri, Feb 14, 2025 at 11:54:52AM -0800, Brian Norris wrote: > On Fri, Feb 14, 2025 at 12:45:52PM +0530, Manivannan Sadhasivam wrote: > > On Tue, Feb 11, 2025 at 04:23:53PM +0800, Tsai Sung-Fu wrote: > > > >Because you cannot set affinity for chained MSIs as these MSIs are muxed to > > > >another parent interrupt. Since the IRQ affinity is all about changing which CPU > > > >gets the IRQ, affinity setting is only possible for the MSI parent. > > > > > > So if we can find the MSI parent by making use of chained > > > relationships (32 MSI vectors muxed to 1 parent), > > > is it possible that we can add that implementation back ? > > > We have another patch that would like to add the > > > dw_pci_msi_set_affinity feature. > > > Would it be a possible try from your perspective ? > > > > > > > This question was brought up plenty of times and the concern from the irqchip > > maintainer Marc was that if you change the affinity of the parent when the child > > MSI affinity changes, it tends to break the userspace ABI of the parent. > > > > See below links: > > > > https://lore.kernel.org/all/87mtg0i8m8.wl-maz@xxxxxxxxxx/ > > https://lore.kernel.org/all/874k0bf7f7.wl-maz@xxxxxxxxxx/ > > It's hard to meaningfully talk about a patch that hasn't been posted > yet, but the implementation we have at least attempts to make *some* > kind of resolution to those ABI questions. For one, it rejects affinity > changes that are incompatible (by some definition) with affinities > requested by other virqs shared on the same parent line. It also updates > their effective affinities upon changes. > > Those replies seem to over-focus on dynamic, user-space initiated > changes too. But how about for "managed-affinity" interrupts? Those are > requested by drivers internally to the kernel (a la > pci_alloc_irq_vectors_affinity()), and can't be changed by user space > afterward. It seems like there'd be room for supporting that, provided > we don't allow conflicting/non-overlapping configurations. > > I do see that Marc sketched out a complex sysfs/hierarchy API in some of > his replies. I'm not sure that would provide too much value to the > managed-affinity cases we're interested in, but I get the appeal for > user-managed affinity. > Whatever your proposal is, please get it reviewed by Marc. - Mani -- மணிவண்ணன் சதாசிவம்
