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[209.132.180.131]) by mx.google.com with ESMTPS id q3-v6si9557063pgv.652.2018.08.31.13.44.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 31 Aug 2018 13:44:01 -0700 (PDT) Received-SPF: pass (google.com: domain of libc-alpha-return-95628-patch=linaro.org@sourceware.org designates 209.132.180.131 as permitted sender) client-ip=209.132.180.131; Authentication-Results: mx.google.com; dkim=pass header.i=@sourceware.org header.s=default header.b=MTo3u6of; dkim=pass header.i=@linaro.org header.s=google header.b=co6Ed1vg; spf=pass (google.com: domain of libc-alpha-return-95628-patch=linaro.org@sourceware.org designates 209.132.180.131 as permitted sender) smtp.mailfrom="libc-alpha-return-95628-patch=linaro.org@sourceware.org"; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linaro.org DomainKey-Signature: a=rsa-sha1; c=nofws; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:from:to:subject:date:message-id:in-reply-to :references; q=dns; s=default; b=O3wqSe6M0USVsuyEVc/piYFv1vmfQMk 5KjcHOop9VBy/BP3hRblCp4tljDrChRWbc6l69bZi94lGODVf9j9SYnkni0ZrK3d Cx4P2jBM8EekYuALucIGitJDntJGi30QjGLkwwJPuxAgYUZIrBhRviH4R7Aa3S/d yt02HjmVcZuo= DKIM-Signature: v=1; a=rsa-sha1; c=relaxed; d=sourceware.org; h=list-id :list-unsubscribe:list-subscribe:list-archive:list-post :list-help:sender:from:to:subject:date:message-id:in-reply-to :references; s=default; bh=7PtU0fx6yI1DV/zKSvbnvYWBoiU=; b=MTo3u 6ofIisxuXWyxU8jf4VliVH645o1gJ9mIYscg5N2uMFxvVYbbbJpY6xWZ/+l+42OK 8pB4GQ7QH31FGpbcXHkMYnW0OEbV2EBJGq/ybr3lfK+U/j6pXRErczPY0Izphwsi Bu+wsw7ycWjXCq7ROfFDRuwE7kZHIoYUjzjQl8= Received: (qmail 55275 invoked by alias); 31 Aug 2018 20:43:01 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Unsubscribe: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Delivered-To: mailing list libc-alpha@sourceware.org Received: (qmail 54954 invoked by uid 89); 31 Aug 2018 20:42:58 -0000 Authentication-Results: sourceware.org; auth=none X-Spam-SWARE-Status: No, score=-22.7 required=5.0 tests=AWL, BAYES_00, GIT_PATCH_0, GIT_PATCH_1, GIT_PATCH_2, GIT_PATCH_3, KAM_SHORT, SEM_URI, SEM_URIRED, SPF_PASS autolearn=ham version=3.3.2 spammy=Engineering, thereby, sorts, pt X-HELO: mail-qk1-f179.google.com DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:subject:date:message-id:in-reply-to:references; bh=uCtF5zLbivX9+6Ksu/PvFhozvTZbblF7X/4ATlKacjk=; b=co6Ed1vg+hLghXaBpZE7XoVzGf9xFXTI0bmwhM8XRgTUjrd+5mDnkrxBcmXfTG7ZKm XytR1Gjn1nB3WfRjQHzklAjb+ao/Q800hQIx2554aXJCf3n6sAyCJzYnUi/TJvGrExhT m4tn2w0E7rupDD/YgUvDE3LxvXzn5YAfI9OIE= Return-Path: From: Adhemerval Zanella To: libc-alpha@sourceware.org Subject: [PATCH v2 5/7] stdlib: Remove use of mergesort on qsort Date: Fri, 31 Aug 2018 17:42:36 -0300 Message-Id: <20180831204238.10626-6-adhemerval.zanella@linaro.org> In-Reply-To: <20180831204238.10626-1-adhemerval.zanella@linaro.org> References: <20180831204238.10626-1-adhemerval.zanella@linaro.org> This patch removes the mergesort optimization on qsort{_r} implementation and use the quicksort instead. The mergesort implementation has some issues: - It is as-safe only for certain types sizes (if total size is less than 1 KB with large element sizes also forcing memory allocation) which contradicts the function documentation. Although not required by the C standard, it is preferable and doable to have a O(1) space implementation. - The malloc for certain element size and element number adds arbitrary latency (might even be worse if malloc is interposed). - To avoid trigger swap from memory allocation the implementation relies on system information that might be virtualized (for instance VMs with overcommit memory) which might leads to potentially use of swap even if system advertise more memory than actually has. The check also have the downside of issuing syscalls where none is expected (although only once per execution). - The mergesort is suboptimal on already sorted array (BZ#21719). The quicksort implementation is already optimized to use constant extra space (due the limit of total number of elements from maximum VM size) and thus can be used to avoid the malloc usage issues. Using bench-qsort (i7-4790K, gcc 7.1.1) shows the performance difference between mergesort (base) and quicksort (patched): Results for member size 4 MostlySorted nmemb | base | patched | diff 32 | 1791 | 2145 | 19.77 4096 | 530267 | 902724 | 70.24 32768 | 5319819 | 7844403 | 47.46 524288 | 105147020 | 152809379 | 45.33 Repeated nmemb | base | patched | diff 32 | 1988 | 2222 | 11.77 4096 | 898057 | 1029244 | 14.61 32768 | 8890765 | 10057897 | 13.13 524288 | 178316071 | 197150076 | 10.56 Sorted nmemb | base | patched | diff 32 | 1511 | 1461 | -3.31 4096 | 277733 | 357884 | 28.86 32768 | 2634360 | 3468080 | 31.65 524288 | 49793076 | 67584959 | 35.73 Unsorted nmemb | base | patched | diff 32 | 2070 | 2385 | 15.22 4096 | 941830 | 1146892 | 21.77 32768 | 9492371 | 10799397 | 13.77 524288 | 191355021 | 212098446 | 10.84 Results for member size 8 MostlySorted nmemb | base | patched | diff 32 | 1763 | 2676 | 51.79 4096 | 510794 | 907769 | 77.72 32768 | 5075103 | 8605499 | 69.56 524288 | 103741137 | 154255341 | 48.69 Repeated nmemb | base | patched | diff 32 | 1908 | 2230 | 16.88 4096 | 904798 | 1129157 | 24.80 32768 | 8954918 | 10775229 | 20.33 524288 | 179825532 | 212935649 | 18.41 Sorted nmemb | base | patched | diff 32 | 1316 | 1193 | -9.35 4096 | 261069 | 308152 | 18.03 32768 | 2449581 | 3022480 | 23.39 524288 | 47772793 | 60029109 | 25.66 Unsorted nmemb | base | patched | diff 32 | 2011 | 2814 | 39.93 4096 | 953723 | 1198160 | 25.63 32768 | 9539278 | 11678920 | 22.43 524288 | 193690362 | 229161344 | 18.31 Results for member size 32 MostlySorted nmemb | base | patched | diff 32 | 4686 | 5073 | 8.26 4096 | 1688822 | 1572437 | -6.89 32768 | 17633569 | 14170732 | -19.64 524288 | 375170630 | 267001863 | -28.83 Repeated nmemb | base | patched | diff 32 | 5138 | 5592 | 8.84 4096 | 2187509 | 1890849 | -13.56 32768 | 22271793 | 18284219 | -17.90 524288 | 468956765 | 361847282 | -22.84 Sorted nmemb | base | patched | diff 32 | 3581 | 1179 | -67.08 4096 | 938145 | 308793 | -67.08 32768 | 9553669 | 3017486 | -68.42 524288 | 194239124 | 63986145 | -67.06 Unsorted nmemb | base | patched | diff 32 | 5235 | 6591 | 25.90 4096 | 2227377 | 1990681 | -10.63 32768 | 22875769 | 19127569 | -16.39 524288 | 484156353 | 375072780 | -22.53 The result shows an increase in latency, as expected. Some performance difference is also due the fact mergesort uses a slight improved swap operation than quicksort (which a following patch addresses it). This change also renders the BZ #21719 fix unrequired (since it is meant to fix the sorted input performance degradation for mergesort). The manual is also updated to indicate the function is now async-cancel safe. Checked on x86_64-linux-gnu. [BZ #21719] * stdlib/Makefile (routines): Remove msort. (CFLAGS-msort.c): Remove rule. * stdlib/msort.c: Remove file. * stdlib/qsort.c (_quicksort): Rename to __qsort_r and add weak_alias to qsort_r. (qsort): New symbol. * manual/argp.texi: Remove qsort @acu* annotation. * manual/locale.texi: Likewise. * manual/search.texi: Likewise. --- manual/argp.texi | 2 +- manual/locale.texi | 3 +- manual/search.texi | 7 +- stdlib/Makefile | 3 +- stdlib/msort.c | 310 --------------------------------------------- stdlib/qsort.c | 15 ++- 6 files changed, 18 insertions(+), 322 deletions(-) delete mode 100644 stdlib/msort.c -- 2.17.1 diff --git a/manual/argp.texi b/manual/argp.texi index 0023441812..b77ad68285 100644 --- a/manual/argp.texi +++ b/manual/argp.texi @@ -735,7 +735,7 @@ for options, bad phase of the moon, etc. @c hol_set_group ok @c hol_find_entry ok @c hol_sort @mtslocale @acucorrupt -@c qsort dup @acucorrupt +@c qsort dup @c hol_entry_qcmp @mtslocale @c hol_entry_cmp @mtslocale @c group_cmp ok diff --git a/manual/locale.texi b/manual/locale.texi index dabb959f9e..15d3b7820c 100644 --- a/manual/locale.texi +++ b/manual/locale.texi @@ -253,7 +253,7 @@ The symbols in this section are defined in the header file @file{locale.h}. @c calculate_head_size ok @c __munmap ok @c compute_hashval ok -@c qsort dup @acucorrupt +@c qsort dup @c rangecmp ok @c malloc @ascuheap @acsmem @c strdup @ascuheap @acsmem @@ -275,7 +275,6 @@ The symbols in this section are defined in the header file @file{locale.h}. @c realloc @ascuheap @acsmem @c realloc @ascuheap @acsmem @c fclose @ascuheap @asulock @acsmem @acsfd @aculock -@c qsort @ascuheap @acsmem @c alias_compare dup @c libc_lock_unlock @aculock @c _nl_explode_name @ascuheap @acsmem diff --git a/manual/search.texi b/manual/search.texi index 57dad7a56d..148d451701 100644 --- a/manual/search.texi +++ b/manual/search.texi @@ -159,7 +159,7 @@ To sort an array using an arbitrary comparison function, use the @deftypefun void qsort (void *@var{array}, size_t @var{count}, size_t @var{size}, comparison_fn_t @var{compare}) @standards{ISO, stdlib.h} -@safety{@prelim{}@mtsafe{}@assafe{}@acunsafe{@acucorrupt{}}} +@safety{@prelim{}@mtsafe{}@assafe{}@acsafe{}} The @code{qsort} function sorts the array @var{array}. The array contains @var{count} elements, each of which is of size @var{size}. @@ -199,9 +199,8 @@ Functions}): The @code{qsort} function derives its name from the fact that it was originally implemented using the ``quick sort'' algorithm. -The implementation of @code{qsort} in this library might not be an -in-place sort and might thereby use an extra amount of memory to store -the array. +The implementation of @code{qsort} in this library is an in-place sort +and uses a constant extra space (allocated on the stack). @end deftypefun @node Search/Sort Example diff --git a/stdlib/Makefile b/stdlib/Makefile index 4e012a865a..2c28033196 100644 --- a/stdlib/Makefile +++ b/stdlib/Makefile @@ -34,7 +34,7 @@ headers := stdlib.h bits/stdlib.h bits/stdlib-ldbl.h bits/stdlib-float.h \ routines := \ atof atoi atol atoll \ abort \ - bsearch qsort msort \ + bsearch qsort \ getenv putenv setenv secure-getenv \ exit on_exit atexit cxa_atexit cxa_finalize old_atexit \ quick_exit at_quick_exit cxa_at_quick_exit cxa_thread_atexit_impl \ @@ -139,7 +139,6 @@ extra-test-objs += tst-putenvmod.os generated += isomac isomac.out tst-putenvmod.so CFLAGS-bsearch.c += $(uses-callbacks) -CFLAGS-msort.c += $(uses-callbacks) CFLAGS-qsort.c += $(uses-callbacks) CFLAGS-system.c += -fexceptions CFLAGS-system.os = -fomit-frame-pointer diff --git a/stdlib/msort.c b/stdlib/msort.c deleted file mode 100644 index 266c2538c0..0000000000 --- a/stdlib/msort.c +++ /dev/null @@ -1,310 +0,0 @@ -/* An alternative to qsort, with an identical interface. - This file is part of the GNU C Library. - Copyright (C) 1992-2018 Free Software Foundation, Inc. - Written by Mike Haertel, September 1988. - - The GNU C Library is free software; you can redistribute it and/or - modify it under the terms of the GNU Lesser General Public - License as published by the Free Software Foundation; either - version 2.1 of the License, or (at your option) any later version. - - The GNU C Library is distributed in the hope that it will be useful, - but WITHOUT ANY WARRANTY; without even the implied warranty of - MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU - Lesser General Public License for more details. - - You should have received a copy of the GNU Lesser General Public - License along with the GNU C Library; if not, see - . */ - -#include -#include -#include -#include -#include -#include -#include -#include - -struct msort_param -{ - size_t s; - size_t var; - __compar_d_fn_t cmp; - void *arg; - char *t; -}; -static void msort_with_tmp (const struct msort_param *p, void *b, size_t n); - -static void -msort_with_tmp (const struct msort_param *p, void *b, size_t n) -{ - char *b1, *b2; - size_t n1, n2; - - if (n <= 1) - return; - - n1 = n / 2; - n2 = n - n1; - b1 = b; - b2 = (char *) b + (n1 * p->s); - - msort_with_tmp (p, b1, n1); - msort_with_tmp (p, b2, n2); - - char *tmp = p->t; - const size_t s = p->s; - __compar_d_fn_t cmp = p->cmp; - void *arg = p->arg; - switch (p->var) - { - case 0: - while (n1 > 0 && n2 > 0) - { - if ((*cmp) (b1, b2, arg) <= 0) - { - *(uint32_t *) tmp = *(uint32_t *) b1; - b1 += sizeof (uint32_t); - --n1; - } - else - { - *(uint32_t *) tmp = *(uint32_t *) b2; - b2 += sizeof (uint32_t); - --n2; - } - tmp += sizeof (uint32_t); - } - break; - case 1: - while (n1 > 0 && n2 > 0) - { - if ((*cmp) (b1, b2, arg) <= 0) - { - *(uint64_t *) tmp = *(uint64_t *) b1; - b1 += sizeof (uint64_t); - --n1; - } - else - { - *(uint64_t *) tmp = *(uint64_t *) b2; - b2 += sizeof (uint64_t); - --n2; - } - tmp += sizeof (uint64_t); - } - break; - case 2: - while (n1 > 0 && n2 > 0) - { - unsigned long *tmpl = (unsigned long *) tmp; - unsigned long *bl; - - tmp += s; - if ((*cmp) (b1, b2, arg) <= 0) - { - bl = (unsigned long *) b1; - b1 += s; - --n1; - } - else - { - bl = (unsigned long *) b2; - b2 += s; - --n2; - } - while (tmpl < (unsigned long *) tmp) - *tmpl++ = *bl++; - } - break; - case 3: - while (n1 > 0 && n2 > 0) - { - if ((*cmp) (*(const void **) b1, *(const void **) b2, arg) <= 0) - { - *(void **) tmp = *(void **) b1; - b1 += sizeof (void *); - --n1; - } - else - { - *(void **) tmp = *(void **) b2; - b2 += sizeof (void *); - --n2; - } - tmp += sizeof (void *); - } - break; - default: - while (n1 > 0 && n2 > 0) - { - if ((*cmp) (b1, b2, arg) <= 0) - { - tmp = (char *) __mempcpy (tmp, b1, s); - b1 += s; - --n1; - } - else - { - tmp = (char *) __mempcpy (tmp, b2, s); - b2 += s; - --n2; - } - } - break; - } - - if (n1 > 0) - memcpy (tmp, b1, n1 * s); - memcpy (b, p->t, (n - n2) * s); -} - - -void -__qsort_r (void *b, size_t n, size_t s, __compar_d_fn_t cmp, void *arg) -{ - size_t size = n * s; - char *tmp = NULL; - struct msort_param p; - - /* For large object sizes use indirect sorting. */ - if (s > 32) - size = 2 * n * sizeof (void *) + s; - - if (size < 1024) - /* The temporary array is small, so put it on the stack. */ - p.t = __alloca (size); - else - { - /* We should avoid allocating too much memory since this might - have to be backed up by swap space. */ - static long int phys_pages; - static int pagesize; - - if (pagesize == 0) - { - phys_pages = __sysconf (_SC_PHYS_PAGES); - - if (phys_pages == -1) - /* Error while determining the memory size. So let's - assume there is enough memory. Otherwise the - implementer should provide a complete implementation of - the `sysconf' function. */ - phys_pages = (long int) (~0ul >> 1); - - /* The following determines that we will never use more than - a quarter of the physical memory. */ - phys_pages /= 4; - - /* Make sure phys_pages is written to memory. */ - atomic_write_barrier (); - - pagesize = __sysconf (_SC_PAGESIZE); - } - - /* Just a comment here. We cannot compute - phys_pages * pagesize - and compare the needed amount of memory against this value. - The problem is that some systems might have more physical - memory then can be represented with a `size_t' value (when - measured in bytes. */ - - /* If the memory requirements are too high don't allocate memory. */ - if (size / pagesize > (size_t) phys_pages) - { - _quicksort (b, n, s, cmp, arg); - return; - } - - /* It's somewhat large, so malloc it. */ - int save = errno; - tmp = malloc (size); - __set_errno (save); - if (tmp == NULL) - { - /* Couldn't get space, so use the slower algorithm - that doesn't need a temporary array. */ - _quicksort (b, n, s, cmp, arg); - return; - } - p.t = tmp; - } - - p.s = s; - p.var = 4; - p.cmp = cmp; - p.arg = arg; - - if (s > 32) - { - /* Indirect sorting. */ - char *ip = (char *) b; - void **tp = (void **) (p.t + n * sizeof (void *)); - void **t = tp; - void *tmp_storage = (void *) (tp + n); - - while ((void *) t < tmp_storage) - { - *t++ = ip; - ip += s; - } - p.s = sizeof (void *); - p.var = 3; - msort_with_tmp (&p, p.t + n * sizeof (void *), n); - - /* tp[0] .. tp[n - 1] is now sorted, copy around entries of - the original array. Knuth vol. 3 (2nd ed.) exercise 5.2-10. */ - char *kp; - size_t i; - for (i = 0, ip = (char *) b; i < n; i++, ip += s) - if ((kp = tp[i]) != ip) - { - size_t j = i; - char *jp = ip; - memcpy (tmp_storage, ip, s); - - do - { - size_t k = (kp - (char *) b) / s; - tp[j] = jp; - memcpy (jp, kp, s); - j = k; - jp = kp; - kp = tp[k]; - } - while (kp != ip); - - tp[j] = jp; - memcpy (jp, tmp_storage, s); - } - } - else - { - if ((s & (sizeof (uint32_t) - 1)) == 0 - && ((char *) b - (char *) 0) % __alignof__ (uint32_t) == 0) - { - if (s == sizeof (uint32_t)) - p.var = 0; - else if (s == sizeof (uint64_t) - && ((char *) b - (char *) 0) % __alignof__ (uint64_t) == 0) - p.var = 1; - else if ((s & (sizeof (unsigned long) - 1)) == 0 - && ((char *) b - (char *) 0) - % __alignof__ (unsigned long) == 0) - p.var = 2; - } - msort_with_tmp (&p, b, n); - } - free (tmp); -} -libc_hidden_def (__qsort_r) -weak_alias (__qsort_r, qsort_r) - - -void -qsort (void *b, size_t n, size_t s, __compar_fn_t cmp) -{ - return __qsort_r (b, n, s, (__compar_d_fn_t) cmp, NULL); -} -libc_hidden_def (qsort) diff --git a/stdlib/qsort.c b/stdlib/qsort.c index 264a06b8a9..b3a5102cac 100644 --- a/stdlib/qsort.c +++ b/stdlib/qsort.c @@ -20,7 +20,6 @@ Engineering a sort function; Jon Bentley and M. Douglas McIlroy; Software - Practice and Experience; Vol. 23 (11), 1249-1265, 1993. */ -#include #include #include #include @@ -86,8 +85,8 @@ typedef struct stack size is needed (actually O(1) in this case)! */ void -_quicksort (void *const pbase, size_t total_elems, size_t size, - __compar_d_fn_t cmp, void *arg) +__qsort_r (void *const pbase, size_t total_elems, size_t size, + __compar_d_fn_t cmp, void *arg) { char *base_ptr = (char *) pbase; @@ -247,3 +246,13 @@ _quicksort (void *const pbase, size_t total_elems, size_t size, } } } + +libc_hidden_def (__qsort_r) +weak_alias (__qsort_r, qsort_r) + +void +qsort (void *b, size_t n, size_t s, __compar_fn_t cmp) +{ + return __qsort_r (b, n, s, (__compar_d_fn_t) cmp, NULL); +} +libc_hidden_def (qsort)