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Date: Tue, 9 Jun 2015 17:18:14 +0530
From: Vineet Gupta <Vineet.Gupta1@...opsys.com>
To: <linux-arch@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC: <arnd@...db.de>, <arc-linux-dev@...opsys.com>,
Vineet Gupta <Vineet.Gupta1@...opsys.com>
Subject: [PATCH 14/28] ARCv2: SMP: ARConnect debug/robustness
- Handle possible interrupt coalescing from MCIP
- chk if prev IPI ack before sending new
Signed-off-by: Vineet Gupta <vgupta@...opsys.com>
---
arch/arc/Kconfig | 15 ++++++++++++---
arch/arc/kernel/mcip.c | 48 ++++++++++++++++++++++++++++++++++++++++++++----
arch/arc/kernel/smp.c | 20 ++++++++++++++++----
3 files changed, 72 insertions(+), 11 deletions(-)
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index 301525020af7..ef5ca5969eaf 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -448,9 +448,10 @@ menuconfig ARC_DBG
bool "ARC debugging"
default y
+if ARC_DBG
+
config ARC_DW2_UNWIND
bool "Enable DWARF specific kernel stack unwind"
- depends on ARC_DBG
default y
select KALLSYMS
help
@@ -464,18 +465,26 @@ config ARC_DW2_UNWIND
config ARC_DBG_TLB_PARANOIA
bool "Paranoia Checks in Low Level TLB Handlers"
- depends on ARC_DBG
default n
config ARC_DBG_TLB_MISS_COUNT
bool "Profile TLB Misses"
default n
select DEBUG_FS
- depends on ARC_DBG
help
Counts number of I and D TLB Misses and exports them via Debugfs
The counters can be cleared via Debugfs as well
+if SMP
+
+config ARC_IPI_DBG
+ bool "Debug Inter Core interrupts"
+ default n
+
+endif
+
+endif
+
config ARC_UBOOT_SUPPORT
bool "Support uboot arg Handling"
default n
diff --git a/arch/arc/kernel/mcip.c b/arch/arc/kernel/mcip.c
index e6ad6e64440a..35921c3ab394 100644
--- a/arch/arc/kernel/mcip.c
+++ b/arch/arc/kernel/mcip.c
@@ -33,27 +33,67 @@ void mcip_init_smp(unsigned int cpu)
static void mcip_ipi_send(int cpu)
{
unsigned long flags;
+ int ipi_was_pending;
+
+ /*
+ * NOTE: We must spin here if the other cpu hasn't yet
+ * serviced a previous message. This can burn lots
+ * of time, but we MUST follows this protocol or
+ * ipi messages can be lost!!!
+ * Also, we must release the lock in this loop because
+ * the other side may get to this same loop and not
+ * be able to ack -- thus causing deadlock.
+ */
+
+ do {
+ raw_spin_lock_irqsave(&mcip_lock, flags);
+ __mcip_cmd(CMD_INTRPT_READ_STATUS, cpu);
+ ipi_was_pending = read_aux_reg(ARC_REG_MCIP_READBACK);
+ if (ipi_was_pending == 0)
+ break; /* break out but keep lock */
+ raw_spin_unlock_irqrestore(&mcip_lock, flags);
+ } while (1);
- raw_spin_lock_irqsave(&mcip_lock, flags);
__mcip_cmd(CMD_INTRPT_GENERATE_IRQ, cpu);
raw_spin_unlock_irqrestore(&mcip_lock, flags);
+
+#ifdef CONFIG_ARC_IPI_DBG
+ if (ipi_was_pending)
+ pr_info("IPI ACK delayed from cpu %d\n", cpu);
+#endif
}
static void mcip_ipi_clear(int irq)
{
- unsigned int cpu;
+ unsigned int cpu, c;
unsigned long flags;
+ unsigned int __maybe_unused copy;
raw_spin_lock_irqsave(&mcip_lock, flags);
/* Who sent the IPI */
__mcip_cmd(CMD_INTRPT_CHECK_SOURCE, 0);
- cpu = read_aux_reg(ARC_REG_MCIP_READBACK); /* 1,2,4,8... */
+ copy = cpu = read_aux_reg(ARC_REG_MCIP_READBACK); /* 1,2,4,8... */
- __mcip_cmd(CMD_INTRPT_GENERATE_ACK, __ffs(cpu)); /* 0,1,2,3... */
+ /*
+ * In rare case, multiple concurrent IPIs sent to same target can
+ * possibly be coalesced by MCIP into 1 asserted IRQ, so @cpus can be
+ * "vectored" (multiple bits sets) as opposed to typical single bit
+ */
+ do {
+ c = __ffs(cpu); /* 0,1,2,3 */
+ __mcip_cmd(CMD_INTRPT_GENERATE_ACK, c);
+ cpu &= ~(1U << c);
+ } while (cpu);
raw_spin_unlock_irqrestore(&mcip_lock, flags);
+
+#ifdef CONFIG_ARC_IPI_DBG
+ if (c != __ffs(copy))
+ pr_info("IPIs from %x coalesced to %x\n",
+ copy, raw_smp_processor_id());
+#endif
}
volatile int wake_flag;
diff --git a/arch/arc/kernel/smp.c b/arch/arc/kernel/smp.c
index d07cb53d7641..be13d12420ba 100644
--- a/arch/arc/kernel/smp.c
+++ b/arch/arc/kernel/smp.c
@@ -278,8 +278,10 @@ static void ipi_cpu_stop(void)
machine_halt();
}
-static inline void __do_IPI(unsigned long msg)
+static inline int __do_IPI(unsigned long msg)
{
+ int rc = 0;
+
switch (msg) {
case IPI_RESCHEDULE:
scheduler_ipi();
@@ -294,8 +296,10 @@ static inline void __do_IPI(unsigned long msg)
break;
default:
- pr_warn("IPI with unexpected msg %ld\n", msg);
+ rc = 1;
}
+
+ return rc;
}
/*
@@ -305,6 +309,7 @@ static inline void __do_IPI(unsigned long msg)
irqreturn_t do_IPI(int irq, void *dev_id)
{
unsigned long pending;
+ unsigned long __maybe_unused copy;
pr_debug("IPI [%ld] received on cpu %d\n",
*this_cpu_ptr(&ipi_data), smp_processor_id());
@@ -316,11 +321,18 @@ irqreturn_t do_IPI(int irq, void *dev_id)
* "dequeue" the msg corresponding to this IPI (and possibly other
* piggybacked msg from elided IPIs: see ipi_send_msg_one() above)
*/
- pending = xchg(this_cpu_ptr(&ipi_data), 0);
+ copy = pending = xchg(this_cpu_ptr(&ipi_data), 0);
do {
unsigned long msg = __ffs(pending);
- __do_IPI(msg);
+ int rc;
+
+ rc = __do_IPI(msg);
+#ifdef CONFIG_ARC_IPI_DBG
+ /* IPI received but no valid @msg */
+ if (rc)
+ pr_info("IPI with bogus msg %ld in %ld\n", msg, copy);
+#endif
pending &= ~(1U << msg);
} while (pending);
--
1.9.1
--
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