cf9bfe55f2
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 a08489c569 "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 <jchandra@broadcom.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/4216/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
151 lines
3.7 KiB
C
151 lines
3.7 KiB
C
/*
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* Count register synchronisation.
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*
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* All CPUs will have their count registers synchronised to the CPU0 next time
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* value. This can cause a small timewarp for CPU0. All other CPU's should
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* not have done anything significant (but they may have had interrupts
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* enabled briefly - prom_smp_finish() should not be responsible for enabling
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* interrupts...)
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*
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* FIXME: broken for SMTC
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*/
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/irqflags.h>
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#include <linux/cpumask.h>
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#include <asm/r4k-timer.h>
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#include <linux/atomic.h>
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#include <asm/barrier.h>
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#include <asm/mipsregs.h>
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static atomic_t __cpuinitdata count_start_flag = ATOMIC_INIT(0);
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static atomic_t __cpuinitdata count_count_start = ATOMIC_INIT(0);
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static atomic_t __cpuinitdata count_count_stop = ATOMIC_INIT(0);
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static atomic_t __cpuinitdata count_reference = ATOMIC_INIT(0);
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#define COUNTON 100
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#define NR_LOOPS 5
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void __cpuinit synchronise_count_master(int cpu)
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{
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int i;
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unsigned long flags;
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unsigned int initcount;
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#ifdef CONFIG_MIPS_MT_SMTC
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/*
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* SMTC needs to synchronise per VPE, not per CPU
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* ignore for now
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*/
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return;
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#endif
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printk(KERN_INFO "Synchronize counters for CPU %u: ", cpu);
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local_irq_save(flags);
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/*
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* Notify the slaves that it's time to start
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*/
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atomic_set(&count_reference, read_c0_count());
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atomic_set(&count_start_flag, cpu);
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smp_wmb();
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/* Count will be initialised to current timer for all CPU's */
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initcount = read_c0_count();
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/*
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* We loop a few times to get a primed instruction cache,
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* then the last pass is more or less synchronised and
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* the master and slaves each set their cycle counters to a known
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* value all at once. This reduces the chance of having random offsets
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* between the processors, and guarantees that the maximum
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* delay between the cycle counters is never bigger than
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* the latency of information-passing (cachelines) between
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* two CPUs.
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*/
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for (i = 0; i < NR_LOOPS; i++) {
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/* slaves loop on '!= 2' */
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while (atomic_read(&count_count_start) != 1)
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mb();
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atomic_set(&count_count_stop, 0);
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smp_wmb();
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/* this lets the slaves write their count register */
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atomic_inc(&count_count_start);
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/*
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* Everyone initialises count in the last loop:
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*/
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if (i == NR_LOOPS-1)
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write_c0_count(initcount);
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/*
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* Wait for all slaves to leave the synchronization point:
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*/
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while (atomic_read(&count_count_stop) != 1)
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mb();
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atomic_set(&count_count_start, 0);
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smp_wmb();
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atomic_inc(&count_count_stop);
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}
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/* Arrange for an interrupt in a short while */
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write_c0_compare(read_c0_count() + COUNTON);
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atomic_set(&count_start_flag, 0);
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local_irq_restore(flags);
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/*
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* i386 code reported the skew here, but the
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* count registers were almost certainly out of sync
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* so no point in alarming people
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*/
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printk("done.\n");
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}
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void __cpuinit synchronise_count_slave(int cpu)
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{
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int i;
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unsigned int initcount;
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#ifdef CONFIG_MIPS_MT_SMTC
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/*
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* SMTC needs to synchronise per VPE, not per CPU
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* ignore for now
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*/
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return;
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#endif
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/*
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* Not every cpu is online at the time this gets called,
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* so we first wait for the master to say everyone is ready
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*/
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while (atomic_read(&count_start_flag) != cpu)
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mb();
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/* Count will be initialised to next expire for all CPU's */
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initcount = atomic_read(&count_reference);
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for (i = 0; i < NR_LOOPS; i++) {
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atomic_inc(&count_count_start);
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while (atomic_read(&count_count_start) != 2)
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mb();
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/*
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* Everyone initialises count in the last loop:
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*/
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if (i == NR_LOOPS-1)
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write_c0_count(initcount);
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atomic_inc(&count_count_stop);
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while (atomic_read(&count_count_stop) != 2)
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mb();
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}
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/* Arrange for an interrupt in a short while */
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write_c0_compare(read_c0_count() + COUNTON);
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}
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#undef NR_LOOPS
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