From: Kevin Wolf <kwolf@redhat.com>
To: anthony@codemonkey.ws
Cc: kwolf@redhat.com, qemu-devel@nongnu.org
Subject: [Qemu-devel] [PATCH 10/18] qemu_img: is_not_zero() optimization
Date: Thu, 19 May 2011 14:33:24 +0200 [thread overview]
Message-ID: <1305808412-16994-11-git-send-email-kwolf@redhat.com> (raw)
In-Reply-To: <1305808412-16994-1-git-send-email-kwolf@redhat.com>
From: Dmitry Konishchev <konishchev@gmail.com>
I run qemu-img under profiler and realized, that most of CPU time is
consumed by is_not_zero() function. I had made a couple of optimizations
on it and got the following output for `time qemu-img convert -O qcow2
volume.qcow2 snapshot.qcow2`:
Original qemu-img:
real 0m56.159s
user 0m34.670s
sys 0m12.079s
Patched qemu-img:
real 0m34.805s
user 0m18.445s
sys 0m12.552s
Signed-off-by: Dmitry Konishchev <konishchev@gmail.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
qemu-img.c | 29 ++++++++++++++++++++++++++---
1 files changed, 26 insertions(+), 3 deletions(-)
diff --git a/qemu-img.c b/qemu-img.c
index 1da5484..4f162d1 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -496,14 +496,37 @@ static int img_commit(int argc, char **argv)
return 0;
}
+/*
+ * Checks whether the sector is not a zero sector.
+ *
+ * Attention! The len must be a multiple of 4 * sizeof(long) due to
+ * restriction of optimizations in this function.
+ */
static int is_not_zero(const uint8_t *sector, int len)
{
+ /*
+ * Use long as the biggest available internal data type that fits into the
+ * CPU register and unroll the loop to smooth out the effect of memory
+ * latency.
+ */
+
int i;
- len >>= 2;
- for(i = 0;i < len; i++) {
- if (((uint32_t *)sector)[i] != 0)
+ long d0, d1, d2, d3;
+ const long * const data = (const long *) sector;
+
+ len /= sizeof(long);
+
+ for(i = 0; i < len; i += 4) {
+ d0 = data[i + 0];
+ d1 = data[i + 1];
+ d2 = data[i + 2];
+ d3 = data[i + 3];
+
+ if (d0 || d1 || d2 || d3) {
return 1;
+ }
}
+
return 0;
}
--
1.7.2.3
next prev parent reply other threads:[~2011-05-19 12:31 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-19 12:33 [Qemu-devel] [PULL 00/18] Block patches Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 01/18] ide: cleanup warnings Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 02/18] posix-aio-compat: Fix idle_threads counter Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 03/18] qemu-img.c: Remove superfluous parenthesis Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 04/18] hw/xen_disk: Remove unused local variable Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 05/18] ide: Turn debug messages into assertions Kevin Wolf
2011-05-26 21:12 ` Luiz Capitulino
2011-05-27 6:39 ` Kevin Wolf
2011-05-27 13:12 ` Luiz Capitulino
2011-06-01 13:44 ` Luiz Capitulino
2011-06-01 14:02 ` Kevin Wolf
2011-06-01 14:07 ` Luiz Capitulino
2011-06-01 15:32 ` Markus Armbruster
2011-06-06 9:08 ` Kevin Wolf
2011-06-06 11:57 ` Markus Armbruster
2011-06-06 12:56 ` Kevin Wolf
2011-06-06 13:52 ` Markus Armbruster
2011-06-06 15:54 ` Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 06/18] Add documentation for qemu_progress_{init, print}() Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 07/18] ahci: Fix crashes on duplicate BH registration Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 08/18] qemu-tool: Stub out qemu-timer functions Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 09/18] qed: Periodically flush and clear need check bit Kevin Wolf
2011-05-19 12:33 ` Kevin Wolf [this message]
2011-05-19 12:33 ` [Qemu-devel] [PATCH 11/18] qed: support for growing images Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 12/18] ide: Split qdev "ide-drive" into "ide-hd" and "ide-cd" Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 13/18] scsi: Split qdev "scsi-disk" into "scsi-hd" and "scsi-cd" Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 14/18] defaults: ide-cd, ide-hd and scsi-cd devices suppress default CD-ROM Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 15/18] block QMP: Deprecate query-block's "type", drop info block's "type=" Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 16/18] blockdev: Store -drive option media in DriveInfo Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 17/18] block: Remove type hint, it's guest matter, doesn't belong here Kevin Wolf
2011-05-19 12:33 ` [Qemu-devel] [PATCH 18/18] ahci: Fix non-NCQ accesses for LBA > 16bits Kevin Wolf
2011-05-19 15:09 ` [Qemu-devel] [PULL 00/18] Block patches Anthony Liguori
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