tools/sched_ext/scx_central.c

   1 /* SPDX-License-Identifier: GPL-2.0 */
   2 /*
   3  * Copyright (c) 2022 Meta Platforms, Inc. and affiliates.
   4  * Copyright (c) 2022 Tejun Heo <tj@kernel.org>
   5  * Copyright (c) 2022 David Vernet <dvernet@meta.com>
   6  */
   7 #define _GNU_SOURCE
   8 #include <sched.h>
   9 #include <stdio.h>
  10 #include <unistd.h>
  11 #include <inttypes.h>
  12 #include <signal.h>
  13 #include <libgen.h>
  14 #include <bpf/bpf.h>
  15 #include <scx/common.h>
  16 #include "scx_central.bpf.skel.h"
  17
  18 const char help_fmt[] =
  19 "A central FIFO sched_ext scheduler.\n"
  20 "\n"
  21 "See the top-level comment in .bpf.c for more details.\n"
  22 "\n"
  23 "Usage: %s [-s SLICE_US] [-c CPU]\n"
  24 "\n"
  25 "  -s SLICE_US   Override slice duration\n"
  26 "  -c CPU        Override the central CPU (default: 0)\n"
  27 "  -v            Print libbpf debug messages\n"
  28 "  -h            Display this help and exit\n";
  29
  30 static bool verbose;
  31 static volatile int exit_req;
  32
  33 static int libbpf_print_fn(enum libbpf_print_level level, const char *format, va_list args)
  34 {
  35         if (level == LIBBPF_DEBUG && !verbose)
  36                 return 0;
  37         return vfprintf(stderr, format, args);
  38 }
  39
  40 static void sigint_handler(int dummy)
  41 {
  42         exit_req = 1;
  43 }
  44
  45 int main(int argc, char **argv)
  46 {
  47         struct scx_central *skel;
  48         struct bpf_link *link;
  49         __u64 seq = 0, ecode;
  50         __s32 opt;
  51         cpu_set_t *cpuset;
  52
  53         libbpf_set_print(libbpf_print_fn);
  54         signal(SIGINT, sigint_handler);
  55         signal(SIGTERM, sigint_handler);
  56 restart:
  57         skel = SCX_OPS_OPEN(central_ops, scx_central);
  58
  59         skel->rodata->central_cpu = 0;
  60         skel->rodata->nr_cpu_ids = libbpf_num_possible_cpus();
  61
  62         while ((opt = getopt(argc, argv, "s:c:pvh")) != -1) {
  63                 switch (opt) {
  64                 case 's':
  65                         skel->rodata->slice_ns = strtoull(optarg, NULL, 0) * 1000;
  66                         break;
  67                 case 'c':
  68                         skel->rodata->central_cpu = strtoul(optarg, NULL, 0);
  69                         break;
  70                 case 'v':
  71                         verbose = true;
  72                         break;
  73                 default:
  74                         fprintf(stderr, help_fmt, basename(argv[0]));
  75                         return opt != 'h';
  76                 }
  77         }
  78
  79         /* Resize arrays so their element count is equal to cpu count. */
  80         RESIZE_ARRAY(skel, data, cpu_gimme_task, skel->rodata->nr_cpu_ids);
  81         RESIZE_ARRAY(skel, data, cpu_started_at, skel->rodata->nr_cpu_ids);
  82
  83         SCX_OPS_LOAD(skel, central_ops, scx_central, uei);
  84
  85         /*
  86          * Affinitize the loading thread to the central CPU, as:
  87          * - That's where the BPF timer is first invoked in the BPF program.
  88          * - We probably don't want this user space component to take up a core
  89          *   from a task that would benefit from avoiding preemption on one of
  90          *   the tickless cores.
  91          *
  92          * Until BPF supports pinning the timer, it's not guaranteed that it
  93          * will always be invoked on the central CPU. In practice, this
  94          * suffices the majority of the time.
  95          */
  96         cpuset = CPU_ALLOC(skel->rodata->nr_cpu_ids);
  97         SCX_BUG_ON(!cpuset, "Failed to allocate cpuset");
  98         CPU_ZERO(cpuset);
  99         CPU_SET(skel->rodata->central_cpu, cpuset);
 100         SCX_BUG_ON(sched_setaffinity(0, sizeof(cpuset), cpuset),
 101                    "Failed to affinitize to central CPU %d (max %d)",
 102                    skel->rodata->central_cpu, skel->rodata->nr_cpu_ids - 1);
 103         CPU_FREE(cpuset);
 104
 105         link = SCX_OPS_ATTACH(skel, central_ops, scx_central);
 106
 107         if (!skel->data->timer_pinned)
 108                 printf("WARNING : BPF_F_TIMER_CPU_PIN not available, timer not pinned to central\n");
 109
 110         while (!exit_req && !UEI_EXITED(skel, uei)) {
 111                 printf("[SEQ %llu]\n", seq++);
 112                 printf("total   :%10" PRIu64 "    local:%10" PRIu64 "   queued:%10" PRIu64 "  lost:%10" PRIu64 "\n",
 113                        skel->bss->nr_total,
 114                        skel->bss->nr_locals,
 115                        skel->bss->nr_queued,
 116                        skel->bss->nr_lost_pids);
 117                 printf("timer   :%10" PRIu64 " dispatch:%10" PRIu64 " mismatch:%10" PRIu64 " retry:%10" PRIu64 "\n",
 118                        skel->bss->nr_timers,
 119                        skel->bss->nr_dispatches,
 120                        skel->bss->nr_mismatches,
 121                        skel->bss->nr_retries);
 122                 printf("overflow:%10" PRIu64 "\n",
 123                        skel->bss->nr_overflows);
 124                 fflush(stdout);
 125                 sleep(1);
 126         }
 127
 128         bpf_link__destroy(link);
 129         ecode = UEI_REPORT(skel, uei);
 130         scx_central__destroy(skel);
 131
 132         if (UEI_ECODE_RESTART(ecode))
 133                 goto restart;
 134         return 0;
 135 }