From cf9bfe55f24973a8f40e2c922a7e82cf09e486fd Mon Sep 17 00:00:00 2001 From: Jayachandran C Date: Tue, 14 Aug 2012 18:56:13 +0530 Subject: MIPS: Synchronize MIPS count one CPU at a time The current implementation of synchronise_count_{master,slave} blocks slave CPUs in early boot until all of them come up. This no longer works because blocking a CPU with interrupts off after notifying the CPU to be online causes problems with the current kernel. Specifically, after the workqueue changes (commit a08489c569dc1 "Pull workqueue changes from Tejun Heo") the CPU_ONLINE notification callback workqueue_cpu_up_callback() will hang on wait_for_completion(&idle_rebind.done), if the slave CPUs are blocked for synchronize_count_slave(). The changes are to update synchronize_count_{master,slave}() to handle one CPU at a time and to call synchronise_count_master() in __cpu_up() so that the CPU_ONLINE notification goes out only after the COP0 COUNT register is synchronized. [ralf@linux-mips.org: This matter only to those few platforms which are using the cp0 counter as their clocksource which are XLP, XLR and MIPS' CMP solution.] Signed-off-by: Jayachandran C Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/4216/ Signed-off-by: Ralf Baechle --- arch/mips/kernel/sync-r4k.c | 26 +++++++++++--------------- 1 file changed, 11 insertions(+), 15 deletions(-) (limited to 'arch/mips/kernel/sync-r4k.c') diff --git a/arch/mips/kernel/sync-r4k.c b/arch/mips/kernel/sync-r4k.c index 842d55e411fd..7f1eca3858de 100644 --- a/arch/mips/kernel/sync-r4k.c +++ b/arch/mips/kernel/sync-r4k.c @@ -28,12 +28,11 @@ static atomic_t __cpuinitdata count_reference = ATOMIC_INIT(0); #define COUNTON 100 #define NR_LOOPS 5 -void __cpuinit synchronise_count_master(void) +void __cpuinit synchronise_count_master(int cpu) { int i; unsigned long flags; unsigned int initcount; - int nslaves; #ifdef CONFIG_MIPS_MT_SMTC /* @@ -43,8 +42,7 @@ void __cpuinit synchronise_count_master(void) return; #endif - printk(KERN_INFO "Synchronize counters across %u CPUs: ", - num_online_cpus()); + printk(KERN_INFO "Synchronize counters for CPU %u: ", cpu); local_irq_save(flags); @@ -52,7 +50,7 @@ void __cpuinit synchronise_count_master(void) * Notify the slaves that it's time to start */ atomic_set(&count_reference, read_c0_count()); - atomic_set(&count_start_flag, 1); + atomic_set(&count_start_flag, cpu); smp_wmb(); /* Count will be initialised to current timer for all CPU's */ @@ -69,10 +67,9 @@ void __cpuinit synchronise_count_master(void) * two CPUs. */ - nslaves = num_online_cpus()-1; for (i = 0; i < NR_LOOPS; i++) { - /* slaves loop on '!= ncpus' */ - while (atomic_read(&count_count_start) != nslaves) + /* slaves loop on '!= 2' */ + while (atomic_read(&count_count_start) != 1) mb(); atomic_set(&count_count_stop, 0); smp_wmb(); @@ -89,7 +86,7 @@ void __cpuinit synchronise_count_master(void) /* * Wait for all slaves to leave the synchronization point: */ - while (atomic_read(&count_count_stop) != nslaves) + while (atomic_read(&count_count_stop) != 1) mb(); atomic_set(&count_count_start, 0); smp_wmb(); @@ -97,6 +94,7 @@ void __cpuinit synchronise_count_master(void) } /* Arrange for an interrupt in a short while */ write_c0_compare(read_c0_count() + COUNTON); + atomic_set(&count_start_flag, 0); local_irq_restore(flags); @@ -108,11 +106,10 @@ void __cpuinit synchronise_count_master(void) printk("done.\n"); } -void __cpuinit synchronise_count_slave(void) +void __cpuinit synchronise_count_slave(int cpu) { int i; unsigned int initcount; - int ncpus; #ifdef CONFIG_MIPS_MT_SMTC /* @@ -127,16 +124,15 @@ void __cpuinit synchronise_count_slave(void) * so we first wait for the master to say everyone is ready */ - while (!atomic_read(&count_start_flag)) + while (atomic_read(&count_start_flag) != cpu) mb(); /* Count will be initialised to next expire for all CPU's */ initcount = atomic_read(&count_reference); - ncpus = num_online_cpus(); for (i = 0; i < NR_LOOPS; i++) { atomic_inc(&count_count_start); - while (atomic_read(&count_count_start) != ncpus) + while (atomic_read(&count_count_start) != 2) mb(); /* @@ -146,7 +142,7 @@ void __cpuinit synchronise_count_slave(void) write_c0_count(initcount); atomic_inc(&count_count_stop); - while (atomic_read(&count_count_stop) != ncpus) + while (atomic_read(&count_count_stop) != 2) mb(); } /* Arrange for an interrupt in a short while */ -- cgit v1.2.1