*
*/
+#include "qemu/osdep.h"
+#include "qemu/host-utils.h"
#include "qemu/buffer.h"
#include "trace.h"
#define BUFFER_MIN_INIT_SIZE 4096
#define BUFFER_MIN_SHRINK_SIZE 65536
+/* define the factor alpha for the exponential smoothing
+ * that is used in the average size calculation. a shift
+ * of 7 results in an alpha of 1/2^7. */
+#define BUFFER_AVG_SIZE_SHIFT 7
+
static size_t buffer_req_size(Buffer *buffer, size_t len)
{
return MAX(BUFFER_MIN_INIT_SIZE,
pow2ceil(buffer->offset + len));
}
+static void buffer_adj_size(Buffer *buffer, size_t len)
+{
+ size_t old = buffer->capacity;
+ buffer->capacity = buffer_req_size(buffer, 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 current 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, ...)
{
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)
{
- size_t old;
-
- /*
- * Only shrink in case the used size is *much* smaller than the
- * capacity, 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;
+ 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 ^ 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 ... */
+ 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));
}
- old = buffer->capacity;
- buffer->capacity = pow2ceil(buffer->offset);
- buffer->capacity = MAX(buffer->capacity, BUFFER_MIN_SHRINK_SIZE);
- buffer->buffer = g_realloc(buffer->buffer, buffer->capacity);
- trace_buffer_resize(buffer->name ?: "unnamed",
- old, buffer->capacity);
+ buffer_adj_size(buffer, 0);
}
void buffer_reserve(Buffer *buffer, size_t len)
{
- size_t old;
-
if ((buffer->capacity - buffer->offset) < len) {
- old = buffer->capacity;
- buffer->capacity = buffer_req_size(buffer, len);
- buffer->buffer = g_realloc(buffer->buffer, buffer->capacity);
- trace_buffer_resize(buffer->name ?: "unnamed",
- old, buffer->capacity);
+ buffer_adj_size(buffer, len);
}
}
void buffer_reset(Buffer *buffer)
{
buffer->offset = 0;
+ buffer_shrink(buffer);
}
void buffer_free(Buffer *buffer)
memmove(buffer->buffer, buffer->buffer + len,
(buffer->offset - len));
buffer->offset -= len;
+ buffer_shrink(buffer);
}
void buffer_move_empty(Buffer *to, Buffer *from)