Date: Tue, 7 Jul 2015 02:17:25 +0000 (UTC) From: Ed Maste <emaste@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-10@freebsd.org Subject: svn commit: r285224 - stable/10/usr.bin/ar Message-ID: <201507070217.t672HPPu051070@repo.freebsd.org>
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Author: emaste Date: Tue Jul 7 02:17:24 2015 New Revision: 285224 URL: https://svnweb.freebsd.org/changeset/base/285224 Log: MFC r284928: speed up ar(1) on UFS file systems Fault in the buffer prior to writing to workaround poor performance due to interaction with kernel fs deadlock avoidance code. See the comment prior to vn_io_fault_doio() in sys/kern/vfs_vnops.c for details of the issue. On my stable/10 desktop with a 16MB obj.o and "ar r out.a obj.o" I see the following run times (seconds): x ar.r284891 + ar.patched +----------------------------------------------------------------------+ |+ | |+ x| |+ xx| |A |A| +----------------------------------------------------------------------+ N Min Max Median Avg Stddev x 3 1.307 1.321 1.315 1.3143333 0.0070237692 + 3 0.020 0.023 0.022 0.021666667 0.0015275252 Difference at 95.0% confidence -1.29267 +/- 0.0115203 -98.3515% +/- 0.876513% (Student's t, pooled s = 0.00508265) Thanks to kib for diagnosing and explaining the issue and suggesting the workaround. Approved by: re (gjb) Sponsored by: The FreeBSD Foundation Modified: stable/10/usr.bin/ar/write.c Directory Properties: stable/10/ (props changed) Modified: stable/10/usr.bin/ar/write.c ============================================================================== --- stable/10/usr.bin/ar/write.c Mon Jul 6 22:55:53 2015 (r285223) +++ stable/10/usr.bin/ar/write.c Tue Jul 7 02:17:24 2015 (r285224) @@ -41,6 +41,7 @@ __FBSDID("$FreeBSD$"); #include <stdlib.h> #include <string.h> #include <sysexits.h> +#include <unistd.h> #include "ar.h" @@ -61,6 +62,7 @@ static void create_symtab_entry(struct b static void free_obj(struct bsdar *bsdar, struct ar_obj *obj); static void insert_obj(struct bsdar *bsdar, struct ar_obj *obj, struct ar_obj *pos); +static void prefault_buffer(const char *buf, size_t s); static void read_objs(struct bsdar *bsdar, const char *archive, int checkargv); static void write_archive(struct bsdar *bsdar, char mode); @@ -551,11 +553,35 @@ write_cleanup(struct bsdar *bsdar) } /* + * Fault in the buffer prior to writing as a workaround for poor performance + * due to interaction with kernel fs deadlock avoidance code. See the comment + * above vn_io_fault_doio() in sys/kern/vfs_vnops.c for details of the issue. + */ +static void +prefault_buffer(const char *buf, size_t s) +{ + volatile const char *p; + size_t page_size; + + if (s == 0) + return; + page_size = sysconf(_SC_PAGESIZE); + for (p = buf; p < buf + s; p += page_size) + *p; + /* + * Ensure we touch the last page as well, in case the buffer is not + * page-aligned. + */ + *(volatile const char *)(buf + s - 1); +} + +/* * Wrapper for archive_write_data(). */ static void write_data(struct bsdar *bsdar, struct archive *a, const void *buf, size_t s) { + prefault_buffer(buf, s); if (archive_write_data(a, buf, s) != (ssize_t)s) bsdar_errc(bsdar, EX_SOFTWARE, 0, "%s", archive_error_string(a));
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