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[PATCH 14/15] Avoid queing multiple reschedule IPI's in SMTC

To: linux-mips@linux-mips.org
Subject: [PATCH 14/15] Avoid queing multiple reschedule IPI's in SMTC
From: Raghu Gandham <raghu@mips.com>
Date: Wed, 01 Jul 2009 19:43:16 -0700
Cc: chris@mips.com
In-reply-to: <20090702023938.23268.65453.stgit@linux-raghu>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20090702023938.23268.65453.stgit@linux-raghu>
Sender: linux-mips-bounce@linux-mips.org
User-agent: StGIT/0.14.3
From: Jaidev Patwardhan <jaidev@mips.com>

Signed-off-by: Chris Dearman <chris@mips.com>
---

 arch/mips/include/asm/smtc_ipi.h |    5 +++--
 arch/mips/kernel/smtc.c          |   33 +++++++++++++++++++++++++++++----
 2 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/arch/mips/include/asm/smtc_ipi.h b/arch/mips/include/asm/smtc_ipi.h
index 8ce5175..832b8be 100644
--- a/arch/mips/include/asm/smtc_ipi.h
+++ b/arch/mips/include/asm/smtc_ipi.h
@@ -23,8 +23,8 @@ struct smtc_ipi {
        void *arg;
        int dest;
 #ifdef SMTC_IPI_DEBUG
-       int sender;
-       long stamp;
+       unsigned sender;
+       unsigned long long stamp;
 #endif /* SMTC_IPI_DEBUG */
 };
 
@@ -45,6 +45,7 @@ struct smtc_ipi_q {
        spinlock_t lock;
        struct smtc_ipi *tail;
        int depth;
+       int resched_flag;       /* reschedule already queued */
 };
 
 static inline void smtc_ipi_nq(struct smtc_ipi_q *q, struct smtc_ipi *p)
diff --git a/arch/mips/kernel/smtc.c b/arch/mips/kernel/smtc.c
index 8a0626c..69240c4 100644
--- a/arch/mips/kernel/smtc.c
+++ b/arch/mips/kernel/smtc.c
@@ -75,7 +75,6 @@ unsigned long irq_hwmask[NR_IRQS];
 
 asiduse smtc_live_asid[MAX_SMTC_TLBS][MAX_SMTC_ASIDS];
 
-
 /*
  * Number of InterProcessor Interrupt (IPI) message buffers to allocate
  */
@@ -388,6 +387,7 @@ void smtc_prepare_cpus(int cpus)
                IPIQ[i].head = IPIQ[i].tail = NULL;
                spin_lock_init(&IPIQ[i].lock);
                IPIQ[i].depth = 0;
+               IPIQ[i].resched_flag = 0; /* No reschedules queued initially */
        }
 
        /* cpu_data index starts at zero */
@@ -738,11 +738,24 @@ void smtc_forward_irq(unsigned int irq)
 static void smtc_ipi_qdump(void)
 {
        int i;
+       struct smtc_ipi *temp;
 
        for (i = 0; i < NR_CPUS ;i++) {
-               printk("IPIQ[%d]: head = 0x%x, tail = 0x%x, depth = %d\n",
+               pr_info("IPIQ[%d]: head = 0x%x, tail = 0x%x, depth = %d\n",
                        i, (unsigned)IPIQ[i].head, (unsigned)IPIQ[i].tail,
                        IPIQ[i].depth);
+               temp = IPIQ[i].head;
+
+               while (temp != IPIQ[i].tail) {
+                       pr_debug("%d %d %d: ", temp->type, temp->dest,
+                              (int)temp->arg);
+#ifdef SMTC_IPI_DEBUG
+                   pr_debug("%u %lu\n", temp->sender, temp->stamp);
+#else
+                   pr_debug("\n");
+#endif
+                   temp = temp->flink;
+               }
        }
 }
 
@@ -781,11 +794,15 @@ void smtc_send_ipi(int cpu, int type, unsigned int action)
        int mtflags;
        unsigned long tcrestart;
        extern void r4k_wait_irqoff(void), __pastwait(void);
+       int set_resched_flag = (type == LINUX_SMP_IPI &&
+                               action == SMP_RESCHEDULE_YOURSELF);
 
        if (cpu == smp_processor_id()) {
                printk("Cannot Send IPI to self!\n");
                return;
        }
+       if (set_resched_flag && IPIQ[cpu].resched_flag != 0)
+               return; /* There is a reschedule queued already */
        /* Set up a descriptor, to be delivered either promptly or queued */
        pipi = smtc_ipi_dq(&freeIPIq);
        if (pipi == NULL) {
@@ -798,6 +815,7 @@ void smtc_send_ipi(int cpu, int type, unsigned int action)
        pipi->dest = cpu;
        if (cpu_data[cpu].vpe_id != cpu_data[smp_processor_id()].vpe_id) {
                /* If not on same VPE, enqueue and send cross-VPE interrupt */
+               IPIQ[cpu].resched_flag |= set_resched_flag;
                smtc_ipi_nq(&IPIQ[cpu], pipi);
                LOCK_CORE_PRA();
                settc(cpu_data[cpu].tc_id);
@@ -844,6 +862,7 @@ void smtc_send_ipi(int cpu, int type, unsigned int action)
                         */
                        write_tc_c0_tchalt(0);
                        UNLOCK_CORE_PRA();
+                       IPIQ[cpu].resched_flag |= set_resched_flag;
                        smtc_ipi_nq(&IPIQ[cpu], pipi);
                } else {
 postdirect:
@@ -993,12 +1012,15 @@ void deferred_smtc_ipi(void)
                 * already enabled.
                 */
                local_irq_save(flags);
-
                spin_lock(&q->lock);
                pipi = __smtc_ipi_dq(q);
                spin_unlock(&q->lock);
-               if (pipi != NULL)
+               if (pipi != NULL) {
+                       if (pipi->type == LINUX_SMP_IPI &&
+                           (int)pipi->arg == SMP_RESCHEDULE_YOURSELF)
+                               IPIQ[q].resched_flag = 0;
                        ipi_decode(pipi);
+               }
                /*
                 * The use of the __raw_local restore isn't
                 * as obviously necessary here as in smtc_ipi_replay(),
@@ -1079,6 +1101,9 @@ static irqreturn_t ipi_interrupt(int irq, void *dev_idm)
                                 * with interrupts off
                                 */
                                local_irq_save(flags);
+                               if (pipi->type == LINUX_SMP_IPI &&
+                                   (int)pipi->arg == SMP_RESCHEDULE_YOURSELF)
+                                       IPIQ[cpu].resched_flag = 0;
                                ipi_decode(pipi);
                                local_irq_restore(flags);
                        }


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