From: Peter Lieven <address@hidden>
the idea behind this patch is to allow the buffer to shrink, but
make this a seldom operation. The buffers average size is measured
exponentionally smoothed with am alpha of 1/128.
Signed-off-by: Peter Lieven <address@hidden>
Signed-off-by: Gerd Hoffmann <address@hidden>
---
include/qemu/buffer.h | 1 +
util/buffer.c | 34 ++++++++++++++++++++++++++++------
2 files changed, 29 insertions(+), 6 deletions(-)
diff --git a/include/qemu/buffer.h b/include/qemu/buffer.h
index 0a69b3a..dead9b7 100644
--- a/include/qemu/buffer.h
+++ b/include/qemu/buffer.h
@@ -37,6 +37,7 @@ struct Buffer {
char *name;
size_t capacity;
size_t offset;
+ uint64_t avg_size;
uint8_t *buffer;
};
diff --git a/util/buffer.c b/util/buffer.c
index fe5a44e..5461f86 100644
--- a/util/buffer.c
+++ b/util/buffer.c
@@ -23,6 +23,7 @@
#define BUFFER_MIN_INIT_SIZE 4096
#define BUFFER_MIN_SHRINK_SIZE 65536
+#define BUFFER_AVG_SIZE_SHIFT 7
static size_t buffer_req_size(Buffer *buffer, size_t len)
{
@@ -37,6 +38,11 @@ static void buffer_adj_size(Buffer *buffer, size_t len)
buffer->buffer = g_realloc(buffer->buffer, buffer->capacity);
trace_buffer_resize(buffer->name ?: "unnamed",
old, buffer->capacity);
+
+ /* make it even harder for the buffer to shrink, reset average size
+ * to currenty capacity if it is larger than the average. */
+ buffer->avg_size = MAX(buffer->avg_size,
+ buffer->capacity << BUFFER_AVG_SIZE_SHIFT);
}
void buffer_init(Buffer *buffer, const char *name, ...)
@@ -48,16 +54,30 @@ void buffer_init(Buffer *buffer, const char *name, ...)
va_end(ap);
}
+static uint64_t buffer_get_avg_size(Buffer *buffer)
+{
+ return buffer->avg_size >> BUFFER_AVG_SIZE_SHIFT;
+}
+
void buffer_shrink(Buffer *buffer)
{
- /*
- * Only shrink in case the used size is *much* smaller than the
- * capacity, to avoid bumping up & down the buffers all the time.
+ size_t new;
+
+ /* Calculate the average size of the buffer as
+ * avg_size = avg_size * ( 1 - a ) + required_size * a
+ * where a is 1 / 2 ^ QIO_BUFFER_AVG_SIZE_SHIFT. */
+ buffer->avg_size *= (1 << BUFFER_AVG_SIZE_SHIFT) - 1;
+ buffer->avg_size >>= BUFFER_AVG_SIZE_SHIFT;
+ buffer->avg_size += buffer_req_size(buffer, 0);
+
+ /* And then only shrink if the average size of the buffer is much
+ * too big, to avoid bumping up & down the buffers all the time.
* realloc() isn't exactly cheap ...
*/
- if (buffer->offset < (buffer->capacity >> 3) &&
- buffer->capacity > BUFFER_MIN_SHRINK_SIZE) {
- return;
+ new = buffer_req_size(buffer, buffer_get_avg_size(buffer));
+ if (new < buffer->capacity >> 3 &&
+ new >= BUFFER_MIN_SHRINK_SIZE) {
+ buffer_adj_size(buffer, buffer_get_avg_size(buffer));
}
buffer_adj_size(buffer, 0);
@@ -83,6 +103,7 @@ uint8_t *buffer_end(Buffer *buffer)
void buffer_reset(Buffer *buffer)
{
buffer->offset = 0;
+ buffer_shrink(buffer);
}
void buffer_free(Buffer *buffer)
@@ -107,6 +128,7 @@ void buffer_advance(Buffer *buffer, size_t len)
memmove(buffer->buffer, buffer->buffer + len,
(buffer->offset - len));
buffer->offset -= len;
+ buffer_shrink(buffer);
}
void buffer_move_empty(Buffer *to, Buffer *from)