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contrib/timerwheel: bad 32-bit, use builtin fls(), fix copyright

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It's bad form to remove other people's copyright and license when you
copy their source for your own use.

Defining BITS_PER_LONG as 64 is incorrect on 32-bit platforms.

The mismatch between the unsigned long of the timer and the int
param to fls() means on 64-bit platforms that any bits set in the
high 32-bits of the the timer are lost/ignored.

gf_tw_find_last_bit() is meant to find the last bit in an array of
longs. It's overkill for gluster's timerwheel  where we only ever pass
a single long; replacing it with a direct call to fls() which is
renamed to gf_tw_fls()

The timer routines are slightly modified from the kernel timer
functions that first appeared circa 2.6.x in .../kernel/timer.c
AFAICT.

find_last_bit() comes from the (linux) kernel (.../lib/find_bit.c
in 4.x kernels, .../lib/find_last_bit.c in 3.x kernels) but as noted
above, it is removed with this patch.

__fls() comes from the linux kernel (.../include/asm-generic/
bitops/{__fls.h,builtin-__fls.h}

Restoring/updating the copyright and license to the version from
the 4.x kernel find_bit.c. (timer.c does not have a license, __fls.h
and builtin-__fls.h do not have a copyright or license, but the whole
kernel is licensed under GPLv2 anyway.)

Change-Id: I2d2defccf1ccc74f55d99e94212747a36a1dff35
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: https://review.gluster.org/17146
Smoke: Gluster Build System <jenkins@build.gluster.org>
NetBSD-regression: NetBSD Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Jeff Darcy <jeff@pl.atyp.us>
This commit is contained in:
Kaleb S. KEITHLEY 2017-05-01 12:39:56 -04:00 committed by Jeff Darcy
parent 93c850dd2a
commit 9d70343977
2 changed files with 66 additions and 71 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

117
contrib/timer-wheel/find_last_bit.c
View File

@ -1,18 +1,20 @@
/*
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.
This program 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 General Public License for more details.
You should have received a copy of the GNU General Public License along
with this program; if not, write to the Free Software Foundation, Inc.,
51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
*/
/* bit search implementation
*
* Copyright (C) 2004 Red Hat, Inc. All Rights Reserved.
* Written by David Howells (dhowells@redhat.com)
*
* Copyright (C) 2008 IBM Corporation
* 'find_last_bit' is written by Rusty Russell <rusty@rustcorp.com.au>
* (Inspired by David Howell's find_next_bit implementation)
*
* Rewritten by Yury Norov <yury.norov@gmail.com> to decrease
* size and improve performance, 2015.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
/**
* @find_last_bit
@ -20,63 +22,40 @@
*/
#ifndef BITS_PER_LONG
#ifdef __LP64__
#define BITS_PER_LONG 64
#else
#define BITS_PER_LONG 32
#endif
#endif
static inline int fls(int x)
unsigned long gw_tw_fls (unsigned long word)
{
int r = 32;
int num = BITS_PER_LONG;
if (!x)
return 0;
if (!(x & 0xffff0000u)) {
x <<= 16;
r -= 16;
}
if (!(x & 0xff000000u)) {
x <<= 8;
r -= 8;
}
if (!(x & 0xf0000000u)) {
x <<= 4;
r -= 4;
}
if (!(x & 0xc0000000u)) {
x <<= 2;
r -= 2;
}
if (!(x & 0x80000000u)) {
x <<= 1;
r -= 1;
}
return r;
}
unsigned long gf_tw_find_last_bit(const unsigned long *addr, unsigned long size)
{
unsigned long words;
unsigned long tmp;
/* Start at final word. */
words = size / BITS_PER_LONG;
/* Partial final word? */
if (size & (BITS_PER_LONG-1)) {
tmp = (addr[words] & (~0UL >> (BITS_PER_LONG
- (size & (BITS_PER_LONG-1)))));
if (tmp)
goto found;
}
while (words) {
tmp = addr[--words];
if (tmp) {
found:
return words * BITS_PER_LONG + fls(tmp);
}
}
/* Not found */
return size;
#if BITS_PER_LONG == 64
if (!(word & (~0ul << 32))) {
num -= 32;
word <<= 32;
}
#endif
if (!(word & (~0ul << (BITS_PER_LONG-16)))) {
num -= 16;
word <<= 16;
}
if (!(word & (~0ul << (BITS_PER_LONG-8)))) {
num -= 8;
word <<= 8;
}
if (!(word & (~0ul << (BITS_PER_LONG-4)))) {
num -= 4;
word <<= 4;
}
if (!(word & (~0ul << (BITS_PER_LONG-2)))) {
num -= 2;
word <<= 2;
}
if (!(word & (~0ul << (BITS_PER_LONG-1))))
num -= 1;
return num;
}

20
contrib/timer-wheel/timer-wheel.c
View File

@ -1,3 +1,11 @@
/*
* linux/kernel/timer.c
*
* Kernel internal timers
*
* Copyright (C) 1991, 1992 Linus Torvalds
*
*/
/*
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
@ -57,9 +65,17 @@ __gf_tw_add_timer (struct tvec_base *base, struct gf_tw_timer_list *timer)
list_add_tail (&timer->entry, vec);
}
/* optimized find_last_bit() */
unsigned long gf_tw_find_last_bit(const unsigned long *, unsigned long);
#if defined(__GNUC__) || defined(__clang__)
static inline unsigned long gf_tw_fls (unsigned long word)
{
return BITS_PER_LONG - __builtin_clzl(word);
}
#else
extern unsigned long gf_tw_fls (unsigned long);
#endif
static inline unsigned long
apply_slack(struct tvec_base *base, struct gf_tw_timer_list *timer)
{
@ -77,7 +93,7 @@ apply_slack(struct tvec_base *base, struct gf_tw_timer_list *timer)
if (mask == 0)
return expires;
int bit = gf_tw_find_last_bit (&mask, BITS_PER_LONG);
int bit = gf_tw_fls (mask);
mask = (1UL << bit) - 1;
expires_limit = expires_limit & ~(mask);