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speed up ar(1) on UFS file systems

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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.

Reviewed by:	eadler, kib
MFC after:	1 week
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D2933
This commit is contained in:
Ed Maste 2015-06-29 13:48:44 +00:00
parent 521987c3e5
commit 01715d8cd1
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=284928
1 changed files with 26 additions and 0 deletions
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26
usr.bin/ar/write.c
View File

@ -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 bsdar *bsdar, void *maddr,
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);
@ -550,12 +552,36 @@ write_cleanup(struct bsdar *bsdar)
bsdar->s_sn = NULL;
}
/*
* 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));