On 19.01.2021 19:41, John Baldwin wrote:
On 1/19/21 8:43 AM, Jessica Clarke wrote:
On 19 Jan 2021, at 00:36, Oleksandr Tymoshenko <[email protected]> wrote:
@@ -142,21 +143,15 @@ static bool irq_assign_cpu = false;
#endif
#endif
-/*
- * - 2 counters for each I/O interrupt.
- * - MAXCPU counters for each IPI counters for SMP.
- */
-#ifdef SMP
-#define INTRCNT_COUNT (NIRQ * 2 + INTR_IPI_COUNT * MAXCPU)
-#else
-#define INTRCNT_COUNT (NIRQ * 2)
-#endif
+int intr_nirq = NIRQ;
+SYSCTL_UINT(_machdep, OID_AUTO, nirq, CTLFLAG_RDTUN, &intr_nirq, 0,
+ "Number of IRQs");
Unsigned integer, given the SYSCTL_UINT?
What's stopping us from dynamically resizing rather than forcing the
user to use a tunable (which also means that, in practice, the limit
will remain unchanged, because you want GENERIC kernels to work out of
the box)?
For x86 (and probably the same here), the biggest headache is that there
is a dynamically allocated array indexed by IRQ value at interrupt
invocation time. Currently it uses no locks since the value of the
pointer is set during boot time and then never changes. Making it
dynamic would require allowing that pointer to change and dealing with
what that entails in a very hot path. Generally speaking, the majority
of interrupts used in a given system are allocated during boot and not
by hotplug devices added post-boot, so there is also not a lot of utility
in having this run-time tunable vs a boot-time tunable.
To be exact, the main headaches are intrcnt and intrnames arrays and
their relationship to the sysctl interface. These fields are used
without locking, they do not have the ability to mark interrupt at given
index as unused. This is the real reason why we can't unload a driver
that acts as an interrupt controller (e.g. USB parallel port with the
possibility of interrupts on each pin).
Everything else in subr_intr.c should be prepared for dynamic
allocation/delete of interrupt sources.
Michal
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