From ec14f4572dfcd6535140a11d26fa0e2fe493f2c0 Mon Sep 17 00:00:00 2001 From: Cyril Hrubis Date: Mon, 22 Jul 2024 16:54:43 +0200 Subject: [PATCH] sched: starvation: Autocallibrate the timeout Instead of hardcoding the values we attempt to measure the CPU speed and set the runtime accordingly. Given that the difference in the duration of the test when the kernel is buggy is about 30x we do not have to have a precise callibration, just very rough estimate if we are running on a server or small ARM board would suffice. So we attempt to measure how long does a bussy loop take and base the default timeout on that. On x86_64 CPUs the resulting runtime seems to be between 2x and 10x of the actual runtime which seems to be in the required range. We also make sure to check the runtime at the end of the test because the failures could have been masked by a timeout multiplier, i.e. if you set LTP_TIMEOUT_MUL=10 the test would previously pass on a buggy kernel as well. The side efect is that we now get better PASS/FAIL messages as well. Signed-off-by: Cyril Hrubis Reviewed-by: Petr Vorel Tested-by: Petr Vorel Tested-by: Anders Roxell --- .../kernel/sched/cfs-scheduler/starvation.c | 41 +++++++++++++++++-- 1 file changed, 38 insertions(+), 3 deletions(-) diff --git a/testcases/kernel/sched/cfs-scheduler/starvation.c b/testcases/kernel/sched/cfs-scheduler/starvation.c index 9ac388fdce5..e707e086562 100644 --- a/testcases/kernel/sched/cfs-scheduler/starvation.c +++ b/testcases/kernel/sched/cfs-scheduler/starvation.c @@ -21,11 +21,38 @@ #include #include "tst_test.h" +#include "tst_safe_clocks.h" +#include "tst_timer.h" static char *str_loop; -static long loop = 2000000; +static long loop = 1000000; static char *str_timeout; -static int timeout = 240; +static int timeout; + +#define CALLIBRATE_LOOPS 120000000 + +static int callibrate(void) +{ + int i; + struct timespec start, stop; + long long diff; + + for (i = 0; i < CALLIBRATE_LOOPS; i++) + __asm__ __volatile__ ("" : "+g" (i) : :); + + SAFE_CLOCK_GETTIME(CLOCK_MONOTONIC_RAW, &start); + + for (i = 0; i < CALLIBRATE_LOOPS; i++) + __asm__ __volatile__ ("" : "+g" (i) : :); + + SAFE_CLOCK_GETTIME(CLOCK_MONOTONIC_RAW, &stop); + + diff = tst_timespec_diff_us(stop, start); + + tst_res(TINFO, "CPU did %i loops in %llius", CALLIBRATE_LOOPS, diff); + + return diff; +} static int wait_for_pid(pid_t pid) { @@ -78,6 +105,8 @@ static void setup(void) if (tst_parse_int(str_timeout, &timeout, 1, INT_MAX)) tst_brk(TBROK, "Invalid number of timeout '%s'", str_timeout); + else + timeout = callibrate() / 1000; tst_set_max_runtime(timeout); } @@ -114,7 +143,13 @@ static void do_test(void) sleep(1); SAFE_KILL(child_pid, SIGTERM); - TST_EXP_PASS(wait_for_pid(child_pid)); + + if (!tst_remaining_runtime()) + tst_res(TFAIL, "Scheduller starvation reproduced."); + else + tst_res(TPASS, "Haven't reproduced scheduller starvation."); + + TST_EXP_PASS_SILENT(wait_for_pid(child_pid)); } static struct tst_test test = {