Hi Thomas, On Wed, 06 Dec 2023 17:47:07 +0100, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > On Sat, Nov 11 2023 at 20:16, Jacob Pan wrote: > > $Subject: x86/vector: Reserve ... > > > Under posted MSIs, all device MSIs are multiplexed into a single CPU > > Under? Will change to "When posted MSIs are enabled, " > > notification vector. MSI handlers will be de-multiplexed at run-time by > > system software without IDT delivery. > > > > This vector has a priority class below the rest of the system vectors. > > Why? I was thinking system interrupt can preempt device posted MSIs. But if nested interrupt is not an option, there is no need. > > Potentially, external vector number space for MSIs can be expanded to > > the entire 0-256 range. > > Don't even mention this. It's wishful thinking and has absolutely > nothing to do with the patch at hand. will remove. > > Signed-off-by: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx> > > --- > > arch/x86/include/asm/irq_vectors.h | 15 ++++++++++++++- > > 1 file changed, 14 insertions(+), 1 deletion(-) > > > > diff --git a/arch/x86/include/asm/irq_vectors.h > > b/arch/x86/include/asm/irq_vectors.h index 3a19904c2db6..077ca38f5a91 > > 100644 --- a/arch/x86/include/asm/irq_vectors.h > > +++ b/arch/x86/include/asm/irq_vectors.h > > @@ -99,9 +99,22 @@ > > > > #define LOCAL_TIMER_VECTOR 0xec > > > > +/* > > + * Posted interrupt notification vector for all device MSIs delivered > > to > > + * the host kernel. > > + * > > + * Choose lower priority class bit [7:4] than other system vectors such > > + * that it can be preempted by the system interrupts. > > That's future music and I'm not convinced at all that we want to allow > nested interrupts with all their implications. Stack depth is the least > of the worries here. There are enough other assumptions about interrupts > not nesting in Linux. > Then, should we allow limited interrupt priority inversion while processing posted MSIs? In the current code, without preemption, we effectively already allow one low priority to block higher ones. I don't know the other worries caused by nested interrupts, still experimenting/studying, but here I am thinking it is just one-deep nesting. Posted MSI notifications are not allowed to nest, so does other system interrupts. > > + * It is also higher than all external vectors but it should not matter > > + * in that external vectors for posted MSIs are in a different number > > space. > > This whole priority muck is pointless. The kernel never used it and will > never use it. OK. Perhaps I didn't make it clear, I am just trying to let system interrupt, such as timer, to preempt posted MSI. Not TPR/PPR etc. > > + */ > > +#define POSTED_MSI_NOTIFICATION_VECTOR 0xdf > > So this just wants to go into the regular system vector number space > until there is a conclusion whether we can and want to allow nested > interrupts. Premature optimization is just creating more confusion than > value. Make sense, for this patchset I didn't include the preemption patch since I am not sure yet. I should use the next system vector. Thanks, Jacob
