Messages in this thread | | | From | (Eric W. Biederman) | Subject | Re: What are the real ioapic rte programming constraints? | Date | Sun, 11 Feb 2007 03:20:18 -0700 |
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Zwane Mwaikambo <zwane@infradead.org> writes:
> On Sat, 10 Feb 2007, Eric W. Biederman wrote: > >> There are not enough details in the justification to really understand >> the issue so I'm asking to see if someone has some more details. >> >> The description makes the assertion that reprograming the ioapic >> when an interrupt is pending is the only safe way to handle this. >> Since edge triggered interrupts cannot be pending at the ioapic I know >> it is not talking level triggered interrupts. >> >> However it is not possible to fully reprogram a level triggered >> interrupt when the interrupt is pending as the ioapic will not >> receive the interrupt acknowledgement. So it turns out I have >> broken this change for several kernel releases without people >> screaming at me about io_apic problems. >> >> Currently I am disabling the irq on the ioapic before reprogramming >> it so I do not run into issues. Does that solve the concerns that >> were patched around by only reprogramming interrupt redirection >> table entry in interrupt handlers? > > Hi Eric, > Could you outline in pseudocode where you're issuing the mask? If > it's done whilst an irq is pending some (intel 7500 based) chipsets will > not actually mask it but treat it as a 'legacy' IRQ and deliver it > anyway. Using the masked whilst pending logic avoids all of that.
The code currently in the kernel does:
pending mask read io_apic ack reprogram vector and destination unmask
So I guess it does retain the bug fix.
What I am looking at doing is:
mask read io_apic -- Past this point no more irqs are expected from the io_apic -- Now I work to drain any inflight/pending instances of the irq send ipi to all irq destinations cpus and wait for it to return read lapic disable local irqs take irq lock -- Now no more irqs are expected to arrive reprogram vector and destination enable local irqs unmask
What I need to ensure is that I have a point where I will not receive any new messages from an ioapic about a particular irq anymore. Even if everything is working perfectly setting the disable bit is not enough because there could be an irq message in flight. So I need to give any in flight irqs a chance to complete.
With a little luck that logic will cover your 7500 disable race as well. If not and there is a reasonable work around we should look at that. This is not a speed critical path so we can afford to do a little more work.
The version of this that I am currently testing is below.
Eric
/* * Synchronize the local APIC and the CPU by doing * a dummy read from the local APIC */ static inline void lapic_sync(void) { apic_read(APIC_ID); }
static void affinity_noop(void *info) { return; }
static void mask_get_irq(unsigned int irq) { struct irq_desc *desc = irq_desc + irq; int cpu;
spin_lock(&vector_lock);
/* * Mask the irq so it will no longer occur */ desc->chip->mask(irq);
/* If I can run a lower priority vector on another cpu * then obviously the irq has completed on that cpu. SMP call * function is lower priority then all of the hardware * irqs. */ for_each_cpu_mask(cpu, desc->affinity) smp_call_function_single(cpu, affinity_noop, NULL, 0, 1);
/* * Ensure irqs have cleared the local cpu */ lapic_sync(); local_irq_disable(); lapic_sync(); spin_lock(&desc->lock); }
static void unmask_put_irq(unsigned int irq) { struct irq_desc *desc = irq_desc + irq;
spin_unlock(&desc->lock); local_irq_enable(); desc->chip->unmask(irq); spin_unlock(&vector_lock); }
static void set_ioapic_affinity_level_irq(unsigned int irq, cpumask_t mask) { unsigned int dest; int vector;
/* * Ensure all of the irq handlers for this irq have completed. * i.e. drain all pending irqs */ mask_get_irq(irq);
cpus_and(mask, mask, cpu_online_map); if (cpus_empty(mask)) goto out;
vector = __assign_irq_vector(irq, mask, &mask); if (vector < 0) goto out;
dest = cpu_mask_to_apicid(mask);
/* * Only the high 8 bits are valid */ dest = SET_APIC_LOGICAL_ID(dest);
spin_lock(&ioapic_lock); __target_IO_APIC_irq(irq, dest, vector); spin_unlock(&ioapic_lock);
set_native_irq_info(irq, mask); out: unmask_put_irq(irq); } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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