Messages in this thread | | | From | "Gowans, James" <> | Subject | Re: [PATCH 2/2] genirq: fasteoi resends interrupt on concurrent invoke | Date | Mon, 5 Jun 2023 16:10:51 +0000 |
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Hi Marc,
On Thu, 2023-06-01 at 09:24 +0200, James Gowans wrote: > While I'm glad that you eventually decided to use the resend mechanism > > instead of spinning on the "old" CPU, I still think imposing this > > behaviour on all users without any discrimination is wrong. > > > > Look at what it does if an interrupt is a wake-up source. You'd > > pointlessly requeue the interrupt (bonus points if the irqchip doesn't > > provide a HW-based retrigger mechanism). > > > > I still maintain that this change should only be applied for the > > particular interrupts that *require* it, and not as a blanket change > > affecting everything under the sun. I have proposed such a change in > > the past, feel free to use it or roll your own. > > Thanks for the example of where this blanket functionality wouldn't be > desired - I'll re-work this to introduce and use > the IRQD_RESEND_WHEN_IN_PROGRESS flag as you originally suggested. > > Just one more thing before I post V3: are you okay with doing the resend > here *after* the handler finished running, and using the IRQ_PENDING flag > to know to resend it? Or would you like it to be resent in > the !irq_may_run(desc) block as you suggested? > > I have a slight preference to do it after, only when we know it's ready to > be run again, and hence not needed to modify check_irq_resend() to cater > for multiple retries.
Hoping/assuming that you're okay with the keeping the resend at the end of the function, here's V3: https://lore.kernel.org/lkml/20230605155723.2628097-2-jgowans@amazon.com/
It's now very close to what to suggested originally. :-)
One thing: I'm not totally sure that it's necessary or correct to set this flag on its_vpe_irq_domain_alloc() too - on my system (r6g.metal Graviton 2 host) that doesn't seem to be run. My guess is that it's for a GIC-v4 system which supports posted interrupt which generally get delivery directly to the vCPU if running, but sometimes need to be delivered to the hypervisor (for example if vCPU not running). I can try test this on r7g.metal which might have GIC-v4 to be sure...
JG
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