ARM: 6488/1: nomadik: prevent sched_clock() wraparound
The current implementation of sched_clock() for the Nomadik family is based on the clock source that will wrap around without any compensation. Currently on the Ux500 after 1030 seconds. Utilize cnt32_to_63 to expand the sched_clock() counter to 63 bits and introduce a keepwarm() timer to assure that sched clock and this cnt32_to_63 is called atleast once every half period. When I print out the actual wrap-around time, and using a year (3600*24*365 seconds) as minumum wrap limit I get an actual wrap-around of: sched_clock: using 55 bits @ 8333125 Hz wrap in 416 days Signed-off-by: Linus Walleij <linus.walleij@stericsson.com> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
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Linus Walleij
Russell King
parent
963fec4e0f
commit
8fbb97a2bc
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@ -3,6 +3,7 @@
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*
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* Copyright (C) 2008 STMicroelectronics
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* Copyright (C) 2010 Alessandro Rubini
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* Copyright (C) 2010 Linus Walleij for ST-Ericsson
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License version 2, as
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@ -16,11 +17,13 @@
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#include <linux/clk.h>
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#include <linux/jiffies.h>
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#include <linux/err.h>
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#include <linux/cnt32_to_63.h>
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#include <linux/timer.h>
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#include <asm/mach/time.h>
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#include <plat/mtu.h>
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void __iomem *mtu_base; /* ssigned by machine code */
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void __iomem *mtu_base; /* Assigned by machine code */
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/*
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* Kernel assumes that sched_clock can be called early
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@ -48,16 +51,82 @@ static struct clocksource nmdk_clksrc = {
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/*
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* Override the global weak sched_clock symbol with this
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* local implementation which uses the clocksource to get some
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* better resolution when scheduling the kernel. We accept that
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* this wraps around for now, since it is just a relative time
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* stamp. (Inspired by OMAP implementation.)
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* better resolution when scheduling the kernel.
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*
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* Because the hardware timer period may be quite short
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* (32.3 secs on the 133 MHz MTU timer selection on ux500)
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* and because cnt32_to_63() needs to be called at least once per
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* half period to work properly, a kernel keepwarm() timer is set up
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* to ensure this requirement is always met.
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*
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* Also the sched_clock timer will wrap around at some point,
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* here we set it to run continously for a year.
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*/
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#define SCHED_CLOCK_MIN_WRAP 3600*24*365
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static struct timer_list cnt32_to_63_keepwarm_timer;
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static u32 sched_mult;
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static u32 sched_shift;
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unsigned long long notrace sched_clock(void)
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{
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return clocksource_cyc2ns(nmdk_clksrc.read(
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&nmdk_clksrc),
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nmdk_clksrc.mult,
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nmdk_clksrc.shift);
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u64 cycles;
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if (unlikely(!mtu_base))
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return 0;
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cycles = cnt32_to_63(-readl(mtu_base + MTU_VAL(0)));
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/*
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* sched_mult is guaranteed to be even so will
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* shift out bit 63
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*/
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return (cycles * sched_mult) >> sched_shift;
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}
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/* Just kick sched_clock every so often */
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static void cnt32_to_63_keepwarm(unsigned long data)
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{
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mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + data));
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(void) sched_clock();
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}
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/*
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* Set up a timer to keep sched_clock():s 32_to_63 algorithm warm
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* once in half a 32bit timer wrap interval.
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*/
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static void __init nmdk_sched_clock_init(unsigned long rate)
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{
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u32 v;
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unsigned long delta;
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u64 days;
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/* Find the apropriate mult and shift factors */
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clocks_calc_mult_shift(&sched_mult, &sched_shift,
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rate, NSEC_PER_SEC, SCHED_CLOCK_MIN_WRAP);
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/* We need to multiply by an even number to get rid of bit 63 */
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if (sched_mult & 1)
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sched_mult++;
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/* Let's see what we get, take max counter and scale it */
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days = (0xFFFFFFFFFFFFFFFFLLU * sched_mult) >> sched_shift;
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do_div(days, NSEC_PER_SEC);
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do_div(days, (3600*24));
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pr_info("sched_clock: using %d bits @ %lu Hz wrap in %lu days\n",
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(64 - sched_shift), rate, (unsigned long) days);
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/*
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* Program a timer to kick us at half 32bit wraparound
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* Formula: seconds per wrap = (2^32) / f
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*/
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v = 0xFFFFFFFFUL / rate;
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/* We want half of the wrap time to keep cnt32_to_63 warm */
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v /= 2;
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pr_debug("sched_clock: prescaled timer rate: %lu Hz, "
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"initialize keepwarm timer every %d seconds\n", rate, v);
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/* Convert seconds to jiffies */
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delta = msecs_to_jiffies(v*1000);
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setup_timer(&cnt32_to_63_keepwarm_timer, cnt32_to_63_keepwarm, delta);
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mod_timer(&cnt32_to_63_keepwarm_timer, round_jiffies(jiffies + delta));
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}
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/* Clockevent device: use one-shot mode */
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@ -161,13 +230,15 @@ void __init nmdk_timer_init(void)
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writel(0, mtu_base + MTU_BGLR(0));
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writel(cr | MTU_CRn_ENA, mtu_base + MTU_CR(0));
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/* Now the scheduling clock is ready */
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/* Now the clock source is ready */
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nmdk_clksrc.read = nmdk_read_timer;
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if (clocksource_register(&nmdk_clksrc))
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pr_err("timer: failed to initialize clock source %s\n",
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nmdk_clksrc.name);
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nmdk_sched_clock_init(rate);
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/* Timer 1 is used for events */
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clockevents_calc_mult_shift(&nmdk_clkevt, rate, MTU_MIN_RANGE);
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