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  • sched_clock: 32 bits at 48MHz, resolution 20ns, wraps every 44739242997ns

    void __init
    sched_clock_register(u64 (*read)(void), int bits, unsigned long rate)
    {
        u64 res, wrap, new_mask, new_epoch, cyc, ns;
        u32 new_mult, new_shift;
        unsigned long r, flags;
        char r_unit;
        struct clock_read_data rd;
    
        if (cd.rate > rate)
            return;
    
        /* Cannot register a sched_clock with interrupts on */
        local_irq_save(flags);
    
        /* Calculate the mult/shift to convert counter ticks to ns. */
        clocks_calc_mult_shift(&new_mult, &new_shift, rate, NSEC_PER_SEC, 3600);
    
        new_mask = CLOCKSOURCE_MASK(bits);
        cd.rate = rate;
    
        /* Calculate how many nanosecs until we risk wrapping */
        wrap = clocks_calc_max_nsecs(new_mult, new_shift, 0, new_mask, NULL);
        cd.wrap_kt = ns_to_ktime(wrap);
    
        rd = cd.read_data[0];
    
        /* Update epoch for new counter and update 'epoch_ns' from old counter*/
        new_epoch = read();
        cyc = cd.actual_read_sched_clock();
        ns = rd.epoch_ns + cyc_to_ns((cyc - rd.epoch_cyc) & rd.sched_clock_mask, rd.mult, rd.shift);
        cd.actual_read_sched_clock = read;
    
        rd.read_sched_clock    = read;
        rd.sched_clock_mask    = new_mask;
        rd.mult            = new_mult;
        rd.shift        = new_shift;
        rd.epoch_cyc        = new_epoch;
        rd.epoch_ns        = ns;
    
        update_clock_read_data(&rd);
    
        if (sched_clock_timer.function != NULL) {
            /* update timeout for clock wrap */
            hrtimer_start(&sched_clock_timer, cd.wrap_kt,
                      HRTIMER_MODE_REL_HARD);
        }
    
        r = rate;
        if (r >= 4000000) {
            r /= 1000000;
            r_unit = 'M';
        } else {
            if (r >= 1000) {
                r /= 1000;
                r_unit = 'k';
            } else {
                r_unit = ' ';
            }
        }
    
        /* Calculate the ns resolution of this counter */
        res = cyc_to_ns(1ULL, new_mult, new_shift);
    
        pr_info("sched_clock: %u bits at %lu%cHz, resolution %lluns, wraps every %lluns\n",
            bits, r, r_unit, res, wrap);
    
        /* Enable IRQ time accounting if we have a fast enough sched_clock() */
        if (irqtime > 0 || (irqtime == -1 && rate >= 1000000))
            enable_sched_clock_irqtime();
    
        local_irq_restore(flags);
    
        pr_debug("Registered %pS as sched_clock source\n", read);
    }
    [    0.219204] clocksource: arm,sp804: mask: 0xffffffff max_cycles: 0xffffffff, max_idle_ns: 39817925974 ns
    [    0.229087] sched_clock: 32 bits at 48MHz, resolution 20ns, wraps every 44739242997ns
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  • 原文地址:https://www.cnblogs.com/dream397/p/15658797.html
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