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drasko |
/*
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* Platform specific perfmon initialization
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*
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* Copyright (C) 2010 B Labs Ltd.
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*
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* Author: Bahadir Balban
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*/
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#include INC_PLAT(timer.h)
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#include <l4/lib/printk.h>
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#include INC_PLAT(offsets.h)
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#include INC_SUBARCH(perfmon.h)
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#include INC_SUBARCH(mmu_ops.h)
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#include INC_GLUE(memlayout.h)
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/*
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* Current findings by these tests:
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*
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* Cpu cycle count and timer ticks are consistently showing 400Mhz
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* with a reference timer tick of 1Mhz. So cycle counts are fixed
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* with regard to the timer.
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*
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* Instruction execute count on the busy_loop however, is varying
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* between x1, x2 combinations when compared to timer and cycle
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* count values. This is happening by trivial changes in code such
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* as adding a function call. (Other variables are ruled out, e.g.
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* no concurrent memory accesses, caches are off)
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*
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* There may be two causes to this:
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* - Due to missing dmb/dsb/isb instructions.
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* - Due to BTC (busy_loop has one branch) which may describe
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* the doubling in IPC, since out of the 2 instructions in the
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* busy loop one is a branch.
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*
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* Disabling the BTC increased cycle counts per instruction
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* significantly, advising us not to expect any accuracy in counting
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* instructions in cycles. Hence instruction-based tests are
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* commented out. It is wise to only rely upon timer and cycle counts.
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*/
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void platform_test_tick_cycles()
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{
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/* Initialize the timer */
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const unsigned int load_value = 0xffffffff - 100000;
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int mhz_top, mhz_bot, temp;
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unsigned long timer_base = PLATFORM_TIMER1_VBASE;
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int cyccnt;
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/* Make sure timer is disabled */
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timer_stop(timer_base);
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/* One shot, 32 bits, no irqs */
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timer_init_oneshot(timer_base);
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/* Load the timer with ticks value */
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timer_load(timer_base, load_value);
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/* Start the timer */
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timer_start(timer_base);
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/* Start counter */
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perfmon_reset_start_cyccnt();
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/* Wait until 0 */
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while (timer_read(timer_base) != 0)
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;
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cyccnt = perfmon_read_cyccnt();
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/* Fixed-point accuracy on bottom digit */
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temp = cyccnt * 64 * 10 * 13 / 100000;
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mhz_top = temp / 10;
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mhz_bot = temp - mhz_top * 10;
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printk("Perfmon: 0x%x cycle count \n", cyccnt);
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printk("%s: %d.%d MHz CPU speed measured by timer REFCLK at 13MHz\n",
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__KERNELNAME__, mhz_top, mhz_bot);
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}
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void platform_test_cpucycles(void)
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{
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/*
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* Variable results:
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*
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* platform_test_loop_cycles();
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* platform_test_loop_ticks();
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*/
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/* Fixed result */
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platform_test_tick_cycles();
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}
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