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If pthread_create() is linked into the binary, then the cosmo runtime will create an independent dlmalloc arena for each core. Whenever the malloc() function is used it will index `g_heaps[sched_getcpu() / 2]` to find the arena with the greatest hyperthread / numa locality. This may be configured via an environment variable. For example if you say `export COSMOPOLITAN_HEAP_COUNT=1` then you can restore the old ways. Your process may be configured to have anywhere between 1 - 128 heaps We need this revision because it makes multithreaded C++ applications faster. For example, an HTTP server I'm working on that makes extreme use of the STL went from 16k to 2000k requests per second, after this change was made. To understand why, try out the malloc_test benchmark which calls malloc() + realloc() in a loop across many threads, which sees a a 250x improvement in process clock time and 200x on wall time The tradeoff is this adds ~25ns of latency to individual malloc calls compared to MODE=tiny, once the cosmo runtime has transitioned into a fully multi-threaded state. If you don't need malloc() to be scalable then cosmo provides many options for you. For starters the heap count variable above can be set to put the process back in single heap mode plus you can go even faster still, if you include tinymalloc.inc like many of the programs in tool/build/.. are already doing since that'll shave tens of kb off your binary footprint too. Theres also MODE=tiny which is configured to use just 1 plain old dlmalloc arena by default Another tradeoff is we need more memory now (except in MODE=tiny), to track the provenance of memory allocation. This is so allocations can be freely shared across threads, and because OSes can reschedule code to different CPUs at any time.
68 lines
3.4 KiB
C
68 lines
3.4 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 2023 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/intrin/magicu.h"
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#include "libc/assert.h"
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/**
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* Precomputes magic numbers for unsigned division by constant.
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*
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* The returned divisor may be passed to __magic_div() to perform
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* unsigned integer division way faster than normal division e.g.
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*
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* assert(77 / 7 == __magicu_div(77, __magicu_get(7)));
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*
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* @param d is intended divisor, which must not be zero
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* @return magic divisor (never zero)
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*/
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struct magicu __magicu_get(uint32_t d) {
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// From Hacker's Delight by Henry S. Warren Jr., 9780321842688
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// Figure 10–3. Simplified algorithm for magic number unsigned
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int a, p;
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struct magicu magu;
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uint32_t p32, q, r, delta;
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npassert(d); // Can't divide by zero.
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p32 = 0; // Avoid compiler warning.
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a = 0; // Initialize "add" indicator.
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p = 31; // Initialize p.
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q = 0x7FFFFFFF / d; // Initialize q = (2**p - 1)/d.
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r = 0x7FFFFFFF - q * d; // Init. r = rem(2**p - 1, d).
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do {
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p = p + 1;
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if (p == 32) {
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p32 = 1; // Set p32 = 2**(p-32).
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} else {
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p32 = 2 * p32;
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}
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if (r + 1 >= d - r) {
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if (q >= 0x7FFFFFFF) a = 1;
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q = 2 * q + 1; // Update q.
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r = 2 * r + 1 - d; // Update r.
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} else {
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if (q >= 0x80000000) a = 1;
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q = 2 * q;
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r = 2 * r + 1;
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}
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delta = d - 1 - r;
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} while (p < 64 && p32 < delta);
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magu.M = q + 1; // Magic number and
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magu.s = p - 32; // Shift amount to return
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if (a) magu.s |= 64; // Sets "add" indicator
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npassert(magu.M || magu.s); // Never returns zero.
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return magu;
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}
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