[MIPS] IRQ Affinity Support for SMTC on Malta Platform (f571eff0) · Commits · git / linux-net

arch/mips/Kconfig

+13 −0

Original line number	Diff line number	Diff line
		@@ -1378,6 +1378,19 @@ config MIPS_MT_SMTC_IM_BACKSTOP
		impact on interrupt service overhead. Disable it only if you know
		what you are doing.

		config MIPS_MT_SMTC_IRQAFF
		bool "Support IRQ affinity API"
		depends on MIPS_MT_SMTC
		default n
		help
		Enables SMP IRQ affinity API (/proc/irq/*/smp_affinity, etc.)
		for SMTC Linux kernel. Requires platform support, of which
		an example can be found in the MIPS kernel i8259 and Malta
		platform code. It is recommended that MIPS_MT_SMTC_INSTANT_REPLAY
		be enabled if MIPS_MT_SMTC_IRQAFF is used. Adds overhead to
		interrupt dispatch, and should be used only if you know what
		you are doing.

		config MIPS_VPE_LOADER_TOM
		bool "Load VPE program into memory hidden from linux"
		depends on MIPS_VPE_LOADER

arch/mips/kernel/i8259.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -39,6 +39,9 @@ static struct irq_chip i8259A_chip = {
		.disable = disable_8259A_irq,
		.unmask = enable_8259A_irq,
		.mask_ack = mask_and_ack_8259A,
		#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
		.set_affinity = plat_set_irq_affinity,
		#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */
		};

		/*

arch/mips/kernel/smtc.c

+63 −0

Original line number	Diff line number	Diff line
		@@ -606,6 +606,60 @@ int setup_irq_smtc(unsigned int irq, struct irqaction * new,
		return setup_irq(irq, new);
		}

		#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
		/*
		* Support for IRQ affinity to TCs
		*/

		void smtc_set_irq_affinity(unsigned int irq, cpumask_t affinity)
		{
		/*
		* If a "fast path" cache of quickly decodable affinity state
		* is maintained, this is where it gets done, on a call up
		* from the platform affinity code.
		*/
		}

		void smtc_forward_irq(unsigned int irq)
		{
		int target;

		/*
		* OK wise guy, now figure out how to get the IRQ
		* to be serviced on an authorized "CPU".
		*
		* Ideally, to handle the situation where an IRQ has multiple
		* eligible CPUS, we would maintain state per IRQ that would
		* allow a fair distribution of service requests. Since the
		* expected use model is any-or-only-one, for simplicity
		* and efficiency, we just pick the easiest one to find.
		*/

		target = first_cpu(irq_desc[irq].affinity);

		/*
		* We depend on the platform code to have correctly processed
		* IRQ affinity change requests to ensure that the IRQ affinity
		* mask has been purged of bits corresponding to nonexistent and
		* offline "CPUs", and to TCs bound to VPEs other than the VPE
		* connected to the physical interrupt input for the interrupt
		* in question. Otherwise we have a nasty problem with interrupt
		* mask management. This is best handled in non-performance-critical
		* platform IRQ affinity setting code, to minimize interrupt-time
		* checks.
		*/

		/* If no one is eligible, service locally */
		if (target >= NR_CPUS) {
		do_IRQ_no_affinity(irq);
		return;
		}

		smtc_send_ipi(target, IRQ_AFFINITY_IPI, irq);
		}

		#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */

		/*
		* IPI model for SMTC is tricky, because interrupts aren't TC-specific.
		* Within a VPE one TC can interrupt another by different approaches.
		@@ -830,6 +884,15 @@ void ipi_decode(struct smtc_ipi *pipi)
		break;
		}
		break;
		#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
		case IRQ_AFFINITY_IPI:
		/*
		* Accept a "forwarded" interrupt that was initially
		* taken by a TC who doesn't have affinity for the IRQ.
		*/
		do_IRQ_no_affinity((int)arg_copy);
		break;
		#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */
		default:
		printk("Impossible SMTC IPI Type 0x%x\n", type_copy);
		break;

arch/mips/mips-boards/malta/malta_smtc.c

+50 −0

Original line number	Diff line number	Diff line
		@@ -88,3 +88,53 @@ void __cpuinit prom_smp_finish(void)
		void prom_cpus_done(void)
		{
		}

		#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
		/*
		* IRQ affinity hook
		*/


		void plat_set_irq_affinity(unsigned int irq, cpumask_t affinity)
		{
		cpumask_t tmask = affinity;
		int cpu = 0;
		void smtc_set_irq_affinity(unsigned int irq, cpumask_t aff);

		/*
		* On the legacy Malta development board, all I/O interrupts
		* are routed through the 8259 and combined in a single signal
		* to the CPU daughterboard, and on the CoreFPGA2/3 34K models,
		* that signal is brought to IP2 of both VPEs. To avoid racing
		* concurrent interrupt service events, IP2 is enabled only on
		* one VPE, by convention VPE0. So long as no bits are ever
		* cleared in the affinity mask, there will never be any
		* interrupt forwarding. But as soon as a program or operator
		* sets affinity for one of the related IRQs, we need to make
		* sure that we don't ever try to forward across the VPE boundry,
		* at least not until we engineer a system where the interrupt
		* _ack() or _end() function can somehow know that it corresponds
		* to an interrupt taken on another VPE, and perform the appropriate
		* restoration of Status.IM state using MFTR/MTTR instead of the
		* normal local behavior. We also ensure that no attempt will
		* be made to forward to an offline "CPU".
		*/

		for_each_cpu_mask(cpu, affinity) {
		if ((cpu_data[cpu].vpe_id != 0) \|\| !cpu_online(cpu))
		cpu_clear(cpu, tmask);
		}
		irq_desc[irq].affinity = tmask;

		if (cpus_empty(tmask))
		/*
		* We could restore a default mask here, but the
		* runtime code can anyway deal with the null set
		*/
		printk(KERN_WARNING
		"IRQ affinity leaves no legal CPU for IRQ %d\n", irq);

		/* Do any generic SMTC IRQ affinity setup */
		smtc_set_irq_affinity(irq, tmask);
		}
		#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */

include/asm-mips/irq.h

+65 −2

Original line number	Diff line number	Diff line
		@@ -46,6 +46,38 @@ static inline void smtc_im_ack_irq(unsigned int irq)

		#endif /* CONFIG_MIPS_MT_SMTC */

		#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
		#include <linux/cpumask.h>

		extern void plat_set_irq_affinity(unsigned int irq, cpumask_t affinity);
		extern void smtc_forward_irq(unsigned int irq);

		/*
		* IRQ affinity hook invoked at the beginning of interrupt dispatch
		* if option is enabled.
		*
		* Up through Linux 2.6.22 (at least) cpumask operations are very
		* inefficient on MIPS. Initial prototypes of SMTC IRQ affinity
		* used a "fast path" per-IRQ-descriptor cache of affinity information
		* to reduce latency. As there is a project afoot to optimize the
		* cpumask implementations, this version is optimistically assuming
		* that cpumask.h macro overhead is reasonable during interrupt dispatch.
		*/
		#define IRQ_AFFINITY_HOOK(irq) \
		do { \
		if (!cpu_isset(smp_processor_id(), irq_desc[irq].affinity)) { \
		smtc_forward_irq(irq); \
		irq_exit(); \
		return; \
		} \
		} while (0)

		#else /* Not doing SMTC affinity */

		#define IRQ_AFFINITY_HOOK(irq) do { } while (0)

		#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */

		#ifdef CONFIG_MIPS_MT_SMTC_IM_BACKSTOP

		/*
		@@ -55,14 +87,28 @@ static inline void smtc_im_ack_irq(unsigned int irq)
		* Otherwise it will be done on return from exception.
		*/
		#define __DO_IRQ_SMTC_HOOK(irq) \
		do { \
		IRQ_AFFINITY_HOOK(irq); \
		if (irq_hwmask[irq] & 0x0000ff00) \
		write_c0_tccontext(read_c0_tccontext() & \
		~(irq_hwmask[irq] & 0x0000ff00)); \
		} while (0)

		#define __NO_AFFINITY_IRQ_SMTC_HOOK(irq) \
		do { \
		if (irq_hwmask[irq] & 0x0000ff00) \
		write_c0_tccontext(read_c0_tccontext() & \
		~(irq_hwmask[irq] & 0x0000ff00)); \
		} while (0)

		#else

		#define __DO_IRQ_SMTC_HOOK(irq) do { } while (0)
		#define __DO_IRQ_SMTC_HOOK(irq) \
		do { \
		IRQ_AFFINITY_HOOK(irq); \
		} while (0)
		#define __NO_AFFINITY_IRQ_SMTC_HOOK(irq) do { } while (0)

		#endif

		/*
		@@ -81,6 +127,23 @@ do { \
		irq_exit(); \
		} while (0)

		#ifdef CONFIG_MIPS_MT_SMTC_IRQAFF
		/*
		* To avoid inefficient and in some cases pathological re-checking of
		* IRQ affinity, we have this variant that skips the affinity check.
		*/


		#define do_IRQ_no_affinity(irq) \
		do { \
		irq_enter(); \
		__NO_AFFINITY_IRQ_SMTC_HOOK(irq); \
		generic_handle_irq(irq); \
		irq_exit(); \
		} while (0)

		#endif /* CONFIG_MIPS_MT_SMTC_IRQAFF */

		extern void arch_init_irq(void);
		extern void spurious_interrupt(void);