3337bf41e0
An extra count on ebb_state.stats.pmc_count[PMC_INDEX(pmc)] is being per- formed when count_pmc() is used to reset PMCs on a few selftests. This extra pmc_count can occasionally invalidate results, such as the ones from cycles_test shown hereafter. The ebb_check_count() failed with an above the upper limit error due to the extra value on ebb_state.stats.pmc_count. Furthermore, this extra count is also indicated by extra PMC1 trace_log on the output of the cycle test (as well as on pmc56_overflow_test): ========== ... [21]: counter = 8 [22]: register SPRN_MMCR0 = 0x0000000080000080 [23]: register SPRN_PMC1 = 0x0000000080000004 [24]: counter = 9 [25]: register SPRN_MMCR0 = 0x0000000080000080 [26]: register SPRN_PMC1 = 0x0000000080000004 [27]: counter = 10 [28]: register SPRN_MMCR0 = 0x0000000080000080 [29]: register SPRN_PMC1 = 0x0000000080000004 >> [30]: register SPRN_PMC1 = 0x000000004000051e PMC1 count (0x280000546) above upper limit 0x2800003e8 (+0x15e) [FAIL] Test FAILED on line 52 failure: cycles ========== Signed-off-by: Desnes A. Nunes do Rosario <desnesn@linux.ibm.com> Tested-by: Sachin Sant <sachinp@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20200626164737.21943-1-desnesn@linux.ibm.com
102 lines
2.3 KiB
C
102 lines
2.3 KiB
C
// SPDX-License-Identifier: GPL-2.0-only
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/*
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* Copyright 2014, Michael Ellerman, IBM Corp.
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*/
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#include <sched.h>
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/mman.h>
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#include "ebb.h"
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/*
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* Test that tries to trigger CPU_FTR_PMAO_BUG. Which is a hardware defect
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* where an exception triggers but we context switch before it is delivered and
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* lose the exception.
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*/
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static int test_body(void)
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{
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int i, orig_period, max_period;
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struct event event;
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SKIP_IF(!ebb_is_supported());
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/* We use PMC4 to make sure the kernel switches all counters correctly */
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event_init_named(&event, 0x40002, "instructions");
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event_leader_ebb_init(&event);
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event.attr.exclude_kernel = 1;
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event.attr.exclude_hv = 1;
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event.attr.exclude_idle = 1;
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FAIL_IF(event_open(&event));
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ebb_enable_pmc_counting(4);
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setup_ebb_handler(standard_ebb_callee);
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ebb_global_enable();
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FAIL_IF(ebb_event_enable(&event));
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/*
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* We want a low sample period, but we also want to get out of the EBB
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* handler without tripping up again.
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*
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* This value picked after much experimentation.
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*/
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orig_period = max_period = sample_period = 400;
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mtspr(SPRN_PMC4, pmc_sample_period(sample_period));
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while (ebb_state.stats.ebb_count < 1000000) {
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/*
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* We are trying to get the EBB exception to race exactly with
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* us entering the kernel to do the syscall. We then need the
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* kernel to decide our timeslice is up and context switch to
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* the other thread. When we come back our EBB will have been
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* lost and we'll spin in this while loop forever.
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*/
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for (i = 0; i < 100000; i++)
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sched_yield();
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/* Change the sample period slightly to try and hit the race */
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if (sample_period >= (orig_period + 200))
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sample_period = orig_period;
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else
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sample_period++;
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if (sample_period > max_period)
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max_period = sample_period;
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}
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ebb_freeze_pmcs();
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ebb_global_disable();
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mtspr(SPRN_PMC4, 0xdead);
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dump_summary_ebb_state();
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dump_ebb_hw_state();
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event_close(&event);
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FAIL_IF(ebb_state.stats.ebb_count == 0);
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/* We vary our sample period so we need extra fudge here */
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FAIL_IF(!ebb_check_count(4, orig_period, 2 * (max_period - orig_period)));
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return 0;
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}
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static int lost_exception(void)
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{
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return eat_cpu(test_body);
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}
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int main(void)
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{
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test_harness_set_timeout(300);
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return test_harness(lost_exception, "lost_exception");
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}
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