qapi/iothread: introduce poll-weight parameter for aio-poll

Introduce a configurable poll-weight parameter for adaptive polling
in IOThread. This parameter replaces the hardcoded POLL_WEIGHT_SHIFT
constant, allowing runtime control over how much the most recent
event interval affects the next polling duration calculation.

The poll-weight parameter uses a shift value where larger values
decrease the weight of the current interval, enabling more gradual
adjustments. When set to 0, a default value of 3 is used (meaning
the current interval contributes approximately 1/8 to the weighted
average).

This patch also removes the hardcoded default value checks from
adjust_polling_time(). Instead, poll-grow, poll-shrink, and
poll-weight now use default values initialized in iothread.c
during IOThread creation.

Signed-off-by: Jaehoon Kim <jhkim@linux.ibm.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20260423195918.661299-4-jhkim@linux.ibm.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

3 files changed, 16 insertions, 25 deletions

diff --git a/util/aio-posix.c b/util/aio-posix.c
index 8e9e9e5d8f..df1c213ce5 100644
--- a/util/aio-posix.c
+++ b/util/aio-posix.c
@@ -29,7 +29,6 @@
 
 /* Stop userspace polling on a handler if it isn't active for some time */
 #define POLL_IDLE_INTERVAL_NS (7 * NANOSECONDS_PER_SECOND)
-#define POLL_WEIGHT_SHIFT   (3)
 
 static void update_handler_poll_times(AioContext *ctx, int64_t block_ns,
                                       int64_t dispatch_time);
@@ -582,28 +581,11 @@ static bool try_poll_mode(AioContext *ctx, AioHandlerList *ready_list,
 
 static void adjust_polling_time(AioContext *ctx, int64_t block_ns)
 {
-    if (block_ns < ctx->poll_ns) {
-        int64_t old = ctx->poll_ns;
-        int64_t shrink = ctx->poll_shrink;
-
-        if (shrink == 0) {
-            shrink = 2;
-        }
-
-        if (block_ns < (ctx->poll_ns / shrink)) {
-            ctx->poll_ns /= shrink;
-        }
-
-        trace_poll_shrink(ctx, old, ctx->poll_ns);
-    } else if (block_ns > ctx->poll_ns) {
+    if (block_ns > ctx->poll_ns) {
         /* There is room to grow, poll longer */
         int64_t old = ctx->poll_ns;
         int64_t grow = ctx->poll_grow;
 
-        if (grow == 0) {
-            grow = 2;
-        }
-
         if (block_ns > ctx->poll_ns * grow) {
             ctx->poll_ns = block_ns;
         } else {
@@ -615,6 +597,11 @@ static void adjust_polling_time(AioContext *ctx, int64_t block_ns)
         }
 
         trace_poll_grow(ctx, old, ctx->poll_ns);
+    } else if (block_ns < (ctx->poll_ns / ctx->poll_shrink)) {
+        int64_t old = ctx->poll_ns;
+        ctx->poll_ns /= ctx->poll_shrink;
+
+        trace_poll_shrink(ctx, old, ctx->poll_ns);
     }
 }
 
@@ -632,8 +619,8 @@ static void update_handler_poll_times(AioContext *ctx, int64_t block_ns,
              * block_ns and previous poll.ns to smooth adjustments.
              */
             node->poll.ns = node->poll.ns
-                ? (node->poll.ns - (node->poll.ns >> POLL_WEIGHT_SHIFT))
-                + (block_ns >> POLL_WEIGHT_SHIFT) : block_ns;
+                ? (node->poll.ns - (node->poll.ns >> ctx->poll_weight))
+                + (block_ns >> ctx->poll_weight) : block_ns;
 
             if (node->poll.ns > ctx->poll_max_ns) {
                 node->poll.ns = 0;
@@ -819,7 +806,8 @@ void aio_context_destroy(AioContext *ctx)
 }
 
 void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
-                                 int64_t grow, int64_t shrink, Error **errp)
+                                 int64_t grow, int64_t shrink,
+                                 int64_t weight, Error **errp)
 {
     AioHandler *node;
 
@@ -833,8 +821,9 @@ void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
      * is used once.
      */
     ctx->poll_max_ns = max_ns;
-    ctx->poll_grow = grow;
-    ctx->poll_shrink = shrink;
+    ctx->poll_grow = (grow ? grow : IOTHREAD_POLL_GROW_DEFAULT);
+    ctx->poll_shrink = (shrink ? shrink : IOTHREAD_POLL_SHRINK_DEFAULT);
+    ctx->poll_weight = (weight ? weight : IOTHREAD_POLL_WEIGHT_DEFAULT);
     ctx->poll_ns = 0;
 
     aio_notify(ctx);
diff --git a/util/aio-win32.c b/util/aio-win32.c
index 6e6f699e4b..1985843233 100644
--- a/util/aio-win32.c
+++ b/util/aio-win32.c
@@ -429,7 +429,8 @@ void aio_context_destroy(AioContext *ctx)
 }
 
 void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,
-                                 int64_t grow, int64_t shrink, Error **errp)
+                                 int64_t grow, int64_t shrink,
+                                 int64_t weight, Error **errp)
 {
     if (max_ns) {
         error_setg(errp, "AioContext polling is not implemented on Windows");
diff --git a/util/async.c b/util/async.c
index 9d3627566f..741fcfd6a7 100644
--- a/util/async.c
+++ b/util/async.c
@@ -609,6 +609,7 @@ AioContext *aio_context_new(Error **errp)
     ctx->poll_ns = 0;
     ctx->poll_grow = 0;
     ctx->poll_shrink = 0;
+    ctx->poll_weight = 0;
 
     ctx->aio_max_batch = 0;