{"id":2220015,"url":"http://patchwork.ozlabs.org/api/1.2/patches/2220015/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260405200735.3075407-4-jhkim@linux.ibm.com/","project":{"id":14,"url":"http://patchwork.ozlabs.org/api/1.2/projects/14/?format=json","name":"QEMU Development","link_name":"qemu-devel","list_id":"qemu-devel.nongnu.org","list_email":"qemu-devel@nongnu.org","web_url":"","scm_url":"","webscm_url":"","list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260405200735.3075407-4-jhkim@linux.ibm.com>","list_archive_url":null,"date":"2026-04-05T20:07:34","name":"[v3,3/3] qapi/iothread: introduce poll-weight parameter for aio-poll","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"e0543498f317026149d83e9f9bd0def2bbb214ee","submitter":{"id":91012,"url":"http://patchwork.ozlabs.org/api/1.2/people/91012/?format=json","name":"Jaehoon Kim","email":"jhkim@linux.ibm.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260405200735.3075407-4-jhkim@linux.ibm.com/mbox/","series":[{"id":498805,"url":"http://patchwork.ozlabs.org/api/1.2/series/498805/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/list/?series=498805","date":"2026-04-05T20:07:32","name":"improve aio-polling efficiency","version":3,"mbox":"http://patchwork.ozlabs.org/series/498805/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2220015/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2220015/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256\n header.s=pp1 header.b=Gwer1odk;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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envelope-from=jhkim@linux.ibm.com;\n helo=mx0a-001b2d01.pphosted.com","X-Spam_score_int":"-26","X-Spam_score":"-2.7","X-Spam_bar":"--","X-Spam_report":"(-2.7 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1,\n DKIM_VALID=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7,\n RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001,\n RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001,\n SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no","X-Spam_action":"no action","X-BeenThere":"qemu-devel@nongnu.org","X-Mailman-Version":"2.1.29","Precedence":"list","List-Id":"qemu development ","List-Unsubscribe":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"},"content":"Introduce a configurable poll-weight parameter for adaptive polling\nin IOThread. This parameter replaces the hardcoded POLL_WEIGHT_SHIFT\nconstant, allowing runtime control over how much the most recent\nevent interval affects the next polling duration calculation.\n\nThe poll-weight parameter uses a shift value where larger values\ndecrease the weight of the current interval, enabling more gradual\nadjustments. When set to 0, a default value of 3 is used (meaning\nthe current interval contributes approximately 1/8 to the weighted\naverage).\n\nThis patch also removes the hardcoded default values for poll-grow\nand poll-shrink parameters from the grow_polling_time() and\nshrink_polling_time() functions, as these defaults are now properly\ninitialized in iothread.c during IOThread creation.\n\nSigned-off-by: Jaehoon Kim \nReviewed-by: Stefan Hajnoczi \n---\n include/qemu/aio.h | 4 ++-\n include/system/iothread.h | 18 ++++++++++++\n iothread.c | 47 ++++++++++++++++++++++---------\n monitor/hmp-cmds.c | 1 +\n qapi/misc.json | 7 +++++\n qapi/qom.json | 10 ++++++-\n qemu-options.hx | 7 ++++-\n tests/unit/test-nested-aio-poll.c | 2 +-\n util/aio-posix.c | 37 +++++++++---------------\n util/aio-win32.c | 3 +-\n util/async.c | 1 +\n 11 files changed, 95 insertions(+), 42 deletions(-)","diff":"diff --git a/include/qemu/aio.h b/include/qemu/aio.h\nindex 6c22064a28..e65e90093a 100644\n--- a/include/qemu/aio.h\n+++ b/include/qemu/aio.h\n@@ -310,6 +310,7 @@ struct AioContext {\n int64_t poll_max_ns; /* maximum polling time in nanoseconds */\n int64_t poll_grow; /* polling time growth factor */\n int64_t poll_shrink; /* polling time shrink factor */\n+ int64_t poll_weight; /* weight of current interval in calculation */\n \n /* AIO engine parameters */\n int64_t aio_max_batch; /* maximum number of requests in a batch */\n@@ -791,12 +792,13 @@ void aio_context_destroy(AioContext *ctx);\n * @max_ns: how long to busy poll for, in nanoseconds\n * @grow: polling time growth factor\n * @shrink: polling time shrink factor\n+ * @weight: weight factor applied to the current polling interval\n *\n * Poll mode can be disabled by setting poll_max_ns to 0.\n */\n void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,\n int64_t grow, int64_t shrink,\n- Error **errp);\n+ int64_t weight, Error **errp);\n \n /**\n * aio_context_set_aio_params:\ndiff --git a/include/system/iothread.h b/include/system/iothread.h\nindex e26d13c6c7..a1ef7696cb 100644\n--- a/include/system/iothread.h\n+++ b/include/system/iothread.h\n@@ -21,6 +21,23 @@\n \n #define TYPE_IOTHREAD \"iothread\"\n \n+#ifdef CONFIG_POSIX\n+/*\n+ * Benchmark results from 2016 on NVMe SSD drives show max polling times around\n+ * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32\n+ * workloads.\n+ */\n+#define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL\n+#define IOTHREAD_POLL_GROW_DEFAULT 2ULL\n+#define IOTHREAD_POLL_SHRINK_DEFAULT 2ULL\n+#define IOTHREAD_POLL_WEIGHT_DEFAULT 3ULL\n+#else\n+#define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL\n+#define IOTHREAD_POLL_GROW_DEFAULT 0ULL\n+#define IOTHREAD_POLL_SHRINK_DEFAULT 0ULL\n+#define IOTHREAD_POLL_WEIGHT_DEFAULT 0ULL\n+#endif\n+\n struct IOThread {\n EventLoopBase parent_obj;\n \n@@ -38,6 +55,7 @@ struct IOThread {\n int64_t poll_max_ns;\n int64_t poll_grow;\n int64_t poll_shrink;\n+ int64_t poll_weight;\n };\n typedef struct IOThread IOThread;\n \ndiff --git a/iothread.c b/iothread.c\nindex caf68e0764..3558535b40 100644\n--- a/iothread.c\n+++ b/iothread.c\n@@ -25,17 +25,6 @@\n #include \"qemu/rcu.h\"\n #include \"qemu/main-loop.h\"\n \n-\n-#ifdef CONFIG_POSIX\n-/* Benchmark results from 2016 on NVMe SSD drives show max polling times around\n- * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32\n- * workloads.\n- */\n-#define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL\n-#else\n-#define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL\n-#endif\n-\n static void *iothread_run(void *opaque)\n {\n IOThread *iothread = opaque;\n@@ -103,6 +92,10 @@ static void iothread_instance_init(Object *obj)\n IOThread *iothread = IOTHREAD(obj);\n \n iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT;\n+ iothread->poll_grow = IOTHREAD_POLL_GROW_DEFAULT;\n+ iothread->poll_shrink = IOTHREAD_POLL_SHRINK_DEFAULT;\n+ iothread->poll_weight = IOTHREAD_POLL_WEIGHT_DEFAULT;\n+\n iothread->thread_id = -1;\n qemu_sem_init(&iothread->init_done_sem, 0);\n /* By default, we don't run gcontext */\n@@ -164,6 +157,7 @@ static void iothread_set_aio_context_params(EventLoopBase *base, Error **errp)\n iothread->poll_max_ns,\n iothread->poll_grow,\n iothread->poll_shrink,\n+ iothread->poll_weight,\n errp);\n if (*errp) {\n return;\n@@ -233,6 +227,9 @@ static IOThreadParamInfo poll_grow_info = {\n static IOThreadParamInfo poll_shrink_info = {\n \"poll-shrink\", offsetof(IOThread, poll_shrink),\n };\n+static IOThreadParamInfo poll_weight_info = {\n+ \"poll-weight\", offsetof(IOThread, poll_weight),\n+};\n \n static void iothread_get_param(Object *obj, Visitor *v,\n const char *name, IOThreadParamInfo *info, Error **errp)\n@@ -254,13 +251,31 @@ static bool iothread_set_param(Object *obj, Visitor *v,\n return false;\n }\n \n- if (value < 0) {\n+ if (info->offset == offsetof(IOThread, poll_weight)) {\n+ if (value < 0 || value > 63) {\n+ error_setg(errp, \"%s value must be in range [0, 63]\",\n+ info->name);\n+ return false;\n+ }\n+ } else if (value < 0) {\n error_setg(errp, \"%s value must be in range [0, %\" PRId64 \"]\",\n info->name, INT64_MAX);\n return false;\n }\n \n- *field = value;\n+ if (value == 0) {\n+ if (info->offset == offsetof(IOThread, poll_grow)) {\n+ *field = IOTHREAD_POLL_GROW_DEFAULT;\n+ } else if (info->offset == offsetof(IOThread, poll_shrink)) {\n+ *field = IOTHREAD_POLL_SHRINK_DEFAULT;\n+ } else if (info->offset == offsetof(IOThread, poll_weight)) {\n+ *field = IOTHREAD_POLL_WEIGHT_DEFAULT;\n+ } else {\n+ *field = value;\n+ }\n+ } else {\n+ *field = value;\n+ }\n \n return true;\n }\n@@ -288,6 +303,7 @@ static void iothread_set_poll_param(Object *obj, Visitor *v,\n iothread->poll_max_ns,\n iothread->poll_grow,\n iothread->poll_shrink,\n+ iothread->poll_weight,\n errp);\n }\n }\n@@ -311,6 +327,10 @@ static void iothread_class_init(ObjectClass *klass, const void *class_data)\n iothread_get_poll_param,\n iothread_set_poll_param,\n NULL, &poll_shrink_info);\n+ object_class_property_add(klass, \"poll-weight\", \"int\",\n+ iothread_get_poll_param,\n+ iothread_set_poll_param,\n+ NULL, &poll_weight_info);\n }\n \n static const TypeInfo iothread_info = {\n@@ -356,6 +376,7 @@ static int query_one_iothread(Object *object, void *opaque)\n info->poll_max_ns = iothread->poll_max_ns;\n info->poll_grow = iothread->poll_grow;\n info->poll_shrink = iothread->poll_shrink;\n+ info->poll_weight = iothread->poll_weight;\n info->aio_max_batch = iothread->parent_obj.aio_max_batch;\n \n QAPI_LIST_APPEND(*tail, info);\ndiff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c\nindex bad034937a..75b6e7fa65 100644\n--- a/monitor/hmp-cmds.c\n+++ b/monitor/hmp-cmds.c\n@@ -206,6 +206,7 @@ void hmp_info_iothreads(Monitor *mon, const QDict *qdict)\n monitor_printf(mon, \" poll-max-ns=%\" PRId64 \"\\n\", value->poll_max_ns);\n monitor_printf(mon, \" poll-grow=%\" PRId64 \"\\n\", value->poll_grow);\n monitor_printf(mon, \" poll-shrink=%\" PRId64 \"\\n\", value->poll_shrink);\n+ monitor_printf(mon, \" poll-weight=%\" PRId64 \"\\n\", value->poll_weight);\n monitor_printf(mon, \" aio-max-batch=%\" PRId64 \"\\n\",\n value->aio_max_batch);\n }\ndiff --git a/qapi/misc.json b/qapi/misc.json\nindex 28c641fe2f..554b0c5717 100644\n--- a/qapi/misc.json\n+++ b/qapi/misc.json\n@@ -85,6 +85,12 @@\n # @poll-shrink: how many ns will be removed from polling time, 0 means\n # that it's not configured (since 2.9)\n #\n+# @poll-weight: the weight factor for adaptive polling.\n+# Determines how much the current event interval contributes to\n+# the next polling time calculation. Valid values are 1 or\n+# greater. 0 selects the system default value which is currently\n+# 3 (since 11.1)\n+#\n # @aio-max-batch: maximum number of requests in a batch for the AIO\n # engine, 0 means that the engine will use its default (since 6.1)\n #\n@@ -96,6 +102,7 @@\n 'poll-max-ns': 'int',\n 'poll-grow': 'int',\n 'poll-shrink': 'int',\n+ 'poll-weight': 'int',\n 'aio-max-batch': 'int' } }\n \n ##\ndiff --git a/qapi/qom.json b/qapi/qom.json\nindex c653248f85..dd45ac1087 100644\n--- a/qapi/qom.json\n+++ b/qapi/qom.json\n@@ -606,6 +606,13 @@\n # algorithm detects it is spending too long polling without\n # encountering events. 0 selects a default behaviour (default: 0)\n #\n+# @poll-weight: the weight factor for adaptive polling. Determines\n+# how much the most recent event interval affects the next\n+# polling duration calculation. If set to 0, the system default\n+# value of 3 is used. Typical values: 1 (high weight on recent\n+# interval), 2-4 (moderate weight on recent interval).\n+# (default: 0) (since 11.1)\n+#\n # The @aio-max-batch option is available since 6.1.\n #\n # Since: 2.0\n@@ -614,7 +621,8 @@\n 'base': 'EventLoopBaseProperties',\n 'data': { '*poll-max-ns': 'int',\n '*poll-grow': 'int',\n- '*poll-shrink': 'int' } }\n+ '*poll-shrink': 'int',\n+ '*poll-weight': 'int' } }\n \n ##\n # @MainLoopProperties:\ndiff --git a/qemu-options.hx b/qemu-options.hx\nindex 69e5a874c1..8ddf6c8d36 100644\n--- a/qemu-options.hx\n+++ b/qemu-options.hx\n@@ -6413,7 +6413,7 @@ SRST\n \n CN=laptop.example.com,O=Example Home,L=London,ST=London,C=GB\n \n- ``-object iothread,id=id,poll-max-ns=poll-max-ns,poll-grow=poll-grow,poll-shrink=poll-shrink,aio-max-batch=aio-max-batch``\n+ ``-object iothread,id=id,poll-max-ns=poll-max-ns,poll-grow=poll-grow,poll-shrink=poll-shrink,poll-weight=poll-weight,aio-max-batch=aio-max-batch``\n Creates a dedicated event loop thread that devices can be\n assigned to. This is known as an IOThread. By default device\n emulation happens in vCPU threads or the main event loop thread.\n@@ -6449,6 +6449,11 @@ SRST\n the polling time when the algorithm detects it is spending too\n long polling without encountering events.\n \n+ The ``poll-weight`` parameter is the weight factor used in the\n+ adaptive polling algorithm. It determines how much the most\n+ recent event interval affects the calculation of the next\n+ polling duration.\n+\n The ``aio-max-batch`` parameter is the maximum number of requests\n in a batch for the AIO engine, 0 means that the engine will use\n its default.\ndiff --git a/tests/unit/test-nested-aio-poll.c b/tests/unit/test-nested-aio-poll.c\nindex 9ab1ad08a7..4c38f36fd4 100644\n--- a/tests/unit/test-nested-aio-poll.c\n+++ b/tests/unit/test-nested-aio-poll.c\n@@ -81,7 +81,7 @@ static void test(void)\n qemu_set_current_aio_context(td.ctx);\n \n /* Enable polling */\n- aio_context_set_poll_params(td.ctx, 1000000, 2, 2, &error_abort);\n+ aio_context_set_poll_params(td.ctx, 1000000, 2, 2, 3, &error_abort);\n \n /* Make the event notifier active (set) right away */\n event_notifier_init(&td.poll_notifier, 1);\ndiff --git a/util/aio-posix.c b/util/aio-posix.c\nindex 8e9e9e5d8f..df1c213ce5 100644\n--- a/util/aio-posix.c\n+++ b/util/aio-posix.c\n@@ -29,7 +29,6 @@\n \n /* Stop userspace polling on a handler if it isn't active for some time */\n #define POLL_IDLE_INTERVAL_NS (7 * NANOSECONDS_PER_SECOND)\n-#define POLL_WEIGHT_SHIFT (3)\n \n static void update_handler_poll_times(AioContext *ctx, int64_t block_ns,\n int64_t dispatch_time);\n@@ -582,28 +581,11 @@ static bool try_poll_mode(AioContext *ctx, AioHandlerList *ready_list,\n \n static void adjust_polling_time(AioContext *ctx, int64_t block_ns)\n {\n- if (block_ns < ctx->poll_ns) {\n- int64_t old = ctx->poll_ns;\n- int64_t shrink = ctx->poll_shrink;\n-\n- if (shrink == 0) {\n- shrink = 2;\n- }\n-\n- if (block_ns < (ctx->poll_ns / shrink)) {\n- ctx->poll_ns /= shrink;\n- }\n-\n- trace_poll_shrink(ctx, old, ctx->poll_ns);\n- } else if (block_ns > ctx->poll_ns) {\n+ if (block_ns > ctx->poll_ns) {\n /* There is room to grow, poll longer */\n int64_t old = ctx->poll_ns;\n int64_t grow = ctx->poll_grow;\n \n- if (grow == 0) {\n- grow = 2;\n- }\n-\n if (block_ns > ctx->poll_ns * grow) {\n ctx->poll_ns = block_ns;\n } else {\n@@ -615,6 +597,11 @@ static void adjust_polling_time(AioContext *ctx, int64_t block_ns)\n }\n \n trace_poll_grow(ctx, old, ctx->poll_ns);\n+ } else if (block_ns < (ctx->poll_ns / ctx->poll_shrink)) {\n+ int64_t old = ctx->poll_ns;\n+ ctx->poll_ns /= ctx->poll_shrink;\n+\n+ trace_poll_shrink(ctx, old, ctx->poll_ns);\n }\n }\n \n@@ -632,8 +619,8 @@ static void update_handler_poll_times(AioContext *ctx, int64_t block_ns,\n * block_ns and previous poll.ns to smooth adjustments.\n */\n node->poll.ns = node->poll.ns\n- ? (node->poll.ns - (node->poll.ns >> POLL_WEIGHT_SHIFT))\n- + (block_ns >> POLL_WEIGHT_SHIFT) : block_ns;\n+ ? (node->poll.ns - (node->poll.ns >> ctx->poll_weight))\n+ + (block_ns >> ctx->poll_weight) : block_ns;\n \n if (node->poll.ns > ctx->poll_max_ns) {\n node->poll.ns = 0;\n@@ -819,7 +806,8 @@ void aio_context_destroy(AioContext *ctx)\n }\n \n void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,\n- int64_t grow, int64_t shrink, Error **errp)\n+ int64_t grow, int64_t shrink,\n+ int64_t weight, Error **errp)\n {\n AioHandler *node;\n \n@@ -833,8 +821,9 @@ void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,\n * is used once.\n */\n ctx->poll_max_ns = max_ns;\n- ctx->poll_grow = grow;\n- ctx->poll_shrink = shrink;\n+ ctx->poll_grow = (grow ? grow : IOTHREAD_POLL_GROW_DEFAULT);\n+ ctx->poll_shrink = (shrink ? shrink : IOTHREAD_POLL_SHRINK_DEFAULT);\n+ ctx->poll_weight = (weight ? weight : IOTHREAD_POLL_WEIGHT_DEFAULT);\n ctx->poll_ns = 0;\n \n aio_notify(ctx);\ndiff --git a/util/aio-win32.c b/util/aio-win32.c\nindex 6e6f699e4b..1985843233 100644\n--- a/util/aio-win32.c\n+++ b/util/aio-win32.c\n@@ -429,7 +429,8 @@ void aio_context_destroy(AioContext *ctx)\n }\n \n void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns,\n- int64_t grow, int64_t shrink, Error **errp)\n+ int64_t grow, int64_t shrink,\n+ int64_t weight, Error **errp)\n {\n if (max_ns) {\n error_setg(errp, \"AioContext polling is not implemented on Windows\");\ndiff --git a/util/async.c b/util/async.c\nindex 9d3627566f..741fcfd6a7 100644\n--- a/util/async.c\n+++ b/util/async.c\n@@ -609,6 +609,7 @@ AioContext *aio_context_new(Error **errp)\n ctx->poll_ns = 0;\n ctx->poll_grow = 0;\n ctx->poll_shrink = 0;\n+ ctx->poll_weight = 0;\n \n ctx->aio_max_batch = 0;\n \n","prefixes":["v3","3/3"]}