160 lines
3.7 KiB
C
160 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 expirelo
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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/r4k-timer.h>
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#include <asm/atomic.h>
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#include <asm/barrier.h>
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#include <asm/cpumask.h>
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#include <asm/mipsregs.h>
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static atomic_t __initdata count_start_flag = ATOMIC_INIT(0);
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static atomic_t __initdata count_count_start = ATOMIC_INIT(0);
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static atomic_t __initdata count_count_stop = ATOMIC_INIT(0);
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#define COUNTON 100
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#define NR_LOOPS 5
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void __init synchronise_count_master(void)
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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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int nslaves;
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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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pr_info("Checking COUNT synchronization across %u CPUs: ",
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num_online_cpus());
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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_start_flag, 1);
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smp_wmb();
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/* Count will be initialised to expirelo for all CPU's */
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initcount = expirelo;
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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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nslaves = num_online_cpus()-1;
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for (i = 0; i < NR_LOOPS; i++) {
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/* slaves loop on '!= ncpus' */
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while (atomic_read(&count_count_start) != nslaves)
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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) != nslaves)
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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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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 __init synchronise_count_slave(void)
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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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int ncpus;
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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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local_irq_save(flags);
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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))
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mb();
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/* Count will be initialised to expirelo for all CPU's */
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initcount = expirelo;
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ncpus = num_online_cpus();
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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) != ncpus)
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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) != ncpus)
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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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local_irq_restore(flags);
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}
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#undef NR_LOOPS
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#endif
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