mirror of
https://github.com/jart/cosmopolitan.git
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56 lines
3 KiB
C
56 lines
3 KiB
C
/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
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│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2022 Justine Alexandra Roberts Tunney │
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│ │
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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│ │
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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╚─────────────────────────────────────────────────────────────────────────────*/
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#include "libc/calls/blockcancel.internal.h"
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#include "libc/calls/calls.h"
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#include "libc/calls/syscall-sysv.internal.h"
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#include "libc/dce.h"
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#include "libc/errno.h"
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#include "libc/runtime/runtime.h"
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#include "libc/str/str.h"
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#include "libc/sysv/consts/at.h"
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#include "libc/sysv/consts/o.h"
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// RDTSC on Linux has so much jitter when the CPU is in powersave mode.
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// Causing things like microbenchmarks to have a 1000% margin of error.
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#define FILE "/sys/devices/system/cpu/cpu0/cpufreq/scaling_governor"
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#define WARN \
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"warning: this operation isn't reliable in powersave mode. please run:\n\t" \
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"echo performance | sudo tee " \
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"/sys/devices/system/cpu/cpu*/cpufreq/scaling_governor\n"
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void __warn_if_powersave(void) {
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if (1)
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return;
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int e, fd;
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char buf[16] = {0};
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if (IsLinux()) {
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e = errno;
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BLOCK_CANCELATION;
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if ((fd = __sys_openat(AT_FDCWD, FILE, O_RDONLY, 0)) != -1) {
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sys_read(fd, buf, 15);
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sys_close(fd);
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if (!startswith(buf, "powersave"))
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return;
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sys_write(2, WARN, sizeof(WARN) - 1);
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}
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ALLOW_CANCELATION;
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errno = e;
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}
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}
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