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[Qemu-devel] [PATCHv3 2/9] cutils: add a function to find non-zero conte
From: |
Peter Lieven |
Subject: |
[Qemu-devel] [PATCHv3 2/9] cutils: add a function to find non-zero content in a buffer |
Date: |
Thu, 21 Mar 2013 16:57:30 +0100 |
this adds buffer_find_nonzero_offset() which is a SSE2/Altives
optimized function that searches for non-zero content in a
buffer.
due to the optimizations used in the function there are restrictions
on buffer address and search length. the function
can_use_buffer_find_nonzero_content() can be used to check if
the function can be used safely.
Signed-off-by: Peter Lieven <address@hidden>
---
include/qemu-common.h | 3 +++
util/cutils.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 53 insertions(+)
diff --git a/include/qemu-common.h b/include/qemu-common.h
index e76ade3..ebbaf71 100644
--- a/include/qemu-common.h
+++ b/include/qemu-common.h
@@ -362,6 +362,9 @@ size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t
offset,
size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
int fillc, size_t bytes);
+#define BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR 8
+inline bool can_use_buffer_find_nonzero_offset(const void *buf, size_t len);
+inline size_t buffer_find_nonzero_offset(const void *buf, size_t len);
bool buffer_is_zero(const void *buf, size_t len);
void qemu_progress_init(int enabled, float min_skip);
diff --git a/util/cutils.c b/util/cutils.c
index 1439da4..6d079ac 100644
--- a/util/cutils.c
+++ b/util/cutils.c
@@ -143,6 +143,56 @@ int qemu_fdatasync(int fd)
}
/*
+ * Searches for an area with non-zero content in a buffer
+ *
+ * Attention! The len must be a multiple of 8 * sizeof(VECTYPE)
+ * and addr must be a multiple of sizeof(VECTYPE) due to
+ * restriction of optimizations in this function.
+ *
+ * can_use_buffer_find_nonzero_offset() can be used to check
+ * these requirements.
+ *
+ * The return value is the offset of the non-zero area rounded
+ * down to 8 * sizeof(VECTYPE). If the buffer is all zero
+ * the return value is equal to len.
+ */
+
+inline size_t buffer_find_nonzero_offset(const void *buf, size_t len)
+{
+ VECTYPE *p = (VECTYPE *)buf;
+ VECTYPE zero = ZERO_SPLAT;
+ size_t i;
+
+ if (*((const long *) buf)) {
+ return 0;
+ }
+
+ for (i = 0; i < len / sizeof(VECTYPE);
+ i += BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR) {
+ VECTYPE tmp0 = p[i + 0] | p[i + 1];
+ VECTYPE tmp1 = p[i + 2] | p[i + 3];
+ VECTYPE tmp2 = p[i + 4] | p[i + 5];
+ VECTYPE tmp3 = p[i + 6] | p[i + 7];
+ VECTYPE tmp01 = tmp0 | tmp1;
+ VECTYPE tmp23 = tmp2 | tmp3;
+ if (!ALL_EQ(tmp01 | tmp23, zero)) {
+ break;
+ }
+ }
+ return i * sizeof(VECTYPE);
+}
+
+inline bool can_use_buffer_find_nonzero_offset(const void *buf, size_t len)
+{
+ if (len % (BUFFER_FIND_NONZERO_OFFSET_UNROLL_FACTOR
+ * sizeof(VECTYPE)) == 0
+ && ((uintptr_t) buf) % sizeof(VECTYPE) == 0) {
+ return true;
+ }
+ return false;
+}
+
+/*
* Checks if a buffer is all zeroes
*
* Attention! The len must be a multiple of 4 * sizeof(long) due to
--
1.7.9.5
- [Qemu-devel] [PATCHv3 1/9] move vector definitions to qemu-common.h, (continued)
- [Qemu-devel] [PATCHv3 1/9] move vector definitions to qemu-common.h, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 4/9] bitops: use vector algorithm to optimize find_next_bit(), Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 8/9] migration: do not search dirty pages in bulk stage, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 7/9] migration: do not sent zero pages in bulk stage, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 2/9] cutils: add a function to find non-zero content in a buffer,
Peter Lieven <=
- [Qemu-devel] [PATCHv3 9/9] migration: use XBZRLE only after bulk stage, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 5/9] migration: search for zero instead of dup pages, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 6/9] migration: add an indicator for bulk state of ram migration, Peter Lieven, 2013/03/21
- [Qemu-devel] [PATCHv3 3/9] buffer_is_zero: use vector optimizations if possible, Peter Lieven, 2013/03/21