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[GFS2] Faster gfs2_bitfit algorithm

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This version of the gfs2_bitfit algorithm includes the latest
suggestions from Steve Whitehouse.  It is typically eight to
ten times faster than the version we're using today.  If there
is a lot of metadata mixed in (lots of small files) the
algorithm is often 15 times faster, and given the right
conditions, I've seen peaks of 20 times faster.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
This commit is contained in:
Bob Peterson 2008-03-10 18:17:47 -05:00 committed by Steven Whitehouse
parent d82661d969
commit 1f466a47e8
1 changed files with 60 additions and 31 deletions
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89
fs/gfs2/rgrp.c
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@ -14,6 +14,7 @@
#include <linux/fs.h>
#include <linux/gfs2_ondisk.h>
#include <linux/lm_interface.h>
#include <linux/prefetch.h>
#include "gfs2.h"
#include "incore.h"
@ -33,6 +34,16 @@
#define BFITNOENT ((u32)~0)
#define NO_BLOCK ((u64)~0)
#if BITS_PER_LONG == 32
#define LBITMASK (0x55555555UL)
#define LBITSKIP55 (0x55555555UL)
#define LBITSKIP00 (0x00000000UL)
#else
#define LBITMASK (0x5555555555555555UL)
#define LBITSKIP55 (0x5555555555555555UL)
#define LBITSKIP00 (0x0000000000000000UL)
#endif
/*
* These routines are used by the resource group routines (rgrp.c)
* to keep track of block allocation. Each block is represented by two
@ -138,45 +149,63 @@ static inline unsigned char gfs2_testbit(struct gfs2_rgrpd *rgd,
static u32 gfs2_bitfit(const u8 *buffer, unsigned int buflen, u32 goal,
u8 old_state)
{
const u8 *byte;
u32 blk = goal;
unsigned int bit, bitlong;
const unsigned long *plong;
#if BITS_PER_LONG == 32
const unsigned long plong55 = 0x55555555;
#else
const unsigned long plong55 = 0x5555555555555555;
#endif
const u8 *byte, *start, *end;
int bit, startbit;
u32 g1, g2, misaligned;
unsigned long *plong;
unsigned long lskipval;
byte = buffer + (goal / GFS2_NBBY);
plong = (const unsigned long *)(buffer + (goal / GFS2_NBBY));
bit = (goal % GFS2_NBBY) * GFS2_BIT_SIZE;
bitlong = bit;
while (byte < buffer + buflen) {
if (bitlong == 0 && old_state == 0 && *plong == plong55) {
plong++;
byte += sizeof(unsigned long);
blk += sizeof(unsigned long) * GFS2_NBBY;
continue;
lskipval = (old_state & GFS2_BLKST_USED) ? LBITSKIP00 : LBITSKIP55;
g1 = (goal / GFS2_NBBY);
start = buffer + g1;
byte = start;
end = buffer + buflen;
g2 = ALIGN(g1, sizeof(unsigned long));
plong = (unsigned long *)(buffer + g2);
startbit = bit = (goal % GFS2_NBBY) * GFS2_BIT_SIZE;
misaligned = g2 - g1;
if (!misaligned)
goto ulong_aligned;
/* parse the bitmap a byte at a time */
misaligned:
while (byte < end) {
if (((*byte >> bit) & GFS2_BIT_MASK) == old_state) {
return goal +
(((byte - start) * GFS2_NBBY) +
((bit - startbit) >> 1));
}
if (((*byte >> bit) & GFS2_BIT_MASK) == old_state)
return blk;
bit += GFS2_BIT_SIZE;
if (bit >= 8) {
if (bit >= GFS2_NBBY * GFS2_BIT_SIZE) {
bit = 0;
byte++;
misaligned--;
if (!misaligned) {
plong = (unsigned long *)byte;
goto ulong_aligned;
}
bitlong += GFS2_BIT_SIZE;
if (bitlong >= sizeof(unsigned long) * 8) {
bitlong = 0;
}
}
return BFITNOENT;
/* parse the bitmap a unsigned long at a time */
ulong_aligned:
/* Stop at "end - 1" or else prefetch can go past the end and segfault.
We could "if" it but we'd lose some of the performance gained.
This way will only slow down searching the very last 4/8 bytes
depending on architecture. I've experimented with several ways
of writing this section such as using an else before the goto
but this one seems to be the fastest. */
while ((unsigned char *)plong < end - 1) {
prefetch(plong + 1);
if (((*plong) & LBITMASK) != lskipval)
break;
plong++;
}
blk++;
if ((unsigned char *)plong < end) {
byte = (const u8 *)plong;
misaligned += sizeof(unsigned long) - 1;
goto misaligned;
}
return BFITNOENT;
}