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[Qemu-devel] [PATCH] bitops: unroll while loop in find_next_bit().
From: |
Peter Lieven |
Subject: |
[Qemu-devel] [PATCH] bitops: unroll while loop in find_next_bit(). |
Date: |
Tue, 12 Mar 2013 08:32:59 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130221 Thunderbird/17.0.3 |
this patch adopts the loop unrolling idea of bitmap_is_zero() to
speed up the skipping of large areas with zeros in find_next_bit().
this routine is extensively used to find dirty pages in
live migration.
testing only the find_next_bit performance on a zeroed bitfield
the loop onrolling decreased executing time by approx. 50% on x86_64.
Signed-off-by: Peter Lieven <address@hidden>
---
util/bitops.c | 18 +++++++++++++++++-
1 file changed, 17 insertions(+), 1 deletion(-)
diff --git a/util/bitops.c b/util/bitops.c
index e72237a..227c38b 100644
--- a/util/bitops.c
+++ b/util/bitops.c
@@ -42,7 +42,23 @@ unsigned long find_next_bit(const unsigned long *addr,
unsigned long size,
size -= BITS_PER_LONG;
result += BITS_PER_LONG;
}
- while (size & ~(BITS_PER_LONG-1)) {
+ while (size >= 4*BITS_PER_LONG) {
+ unsigned long d1, d2, d3;
+ tmp = *p;
+ d1 = *(p+1);
+ d2 = *(p+2);
+ d3 = *(p+3);
+ if (tmp) {
+ goto found_middle;
+ }
+ if (d1 | d2 | d3) {
+ break;
+ }
+ p += 4;
+ result += 4*BITS_PER_LONG;
+ size -= 4*BITS_PER_LONG;
+ }
+ while (size >= BITS_PER_LONG) {
if ((tmp = *(p++))) {
goto found_middle;
}
--
1.7.9.5
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, (continued)
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Peter Lieven, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Peter Lieven, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Paolo Bonzini, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Peter Lieven, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Paolo Bonzini, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Peter Lieven, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Paolo Bonzini, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, ronnie sahlberg, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Paolo Bonzini, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Peter Lieven, 2013/03/11
- [Qemu-devel] [PATCH] bitops: unroll while loop in find_next_bit().,
Peter Lieven <=
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Peter Maydell, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Peter Maydell, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Peter Lieven, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Paolo Bonzini, 2013/03/11
- Re: [Qemu-devel] [RFC] find_next_bit optimizations, Peter Lieven, 2013/03/11
Re: [Qemu-devel] [RFC] find_next_bit optimizations, Stefan Hajnoczi, 2013/03/12