From: Jaehoon Kim <[email protected]> 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 <[email protected]> Reviewed-by: Stefan Hajnoczi <[email protected]> Acked-by: Markus Armbruster <[email protected]> Message-ID: <[email protected]> Signed-off-by: Stefan Hajnoczi <[email protected]> --- qapi/misc.json | 6 ++++ qapi/qom.json | 10 ++++++- include/qemu/aio.h | 4 ++- include/system/iothread.h | 18 ++++++++++++ iothread.c | 47 ++++++++++++++++++++++--------- monitor/hmp-cmds.c | 1 + tests/unit/test-nested-aio-poll.c | 2 +- util/aio-posix.c | 37 +++++++++--------------- util/aio-win32.c | 3 +- util/async.c | 1 + qemu-options.hx | 8 +++++- 11 files changed, 95 insertions(+), 42 deletions(-) diff --git a/qapi/misc.json b/qapi/misc.json index 28c641fe2f..22b7afed9f 100644 --- a/qapi/misc.json +++ b/qapi/misc.json @@ -85,6 +85,11 @@ # @poll-shrink: how many ns will be removed from polling time, 0 means # that it's not configured (since 2.9) # +# @poll-weight: the weight factor for adaptive polling. +# Determines how much the current event interval contributes to +# the next polling time calculation. Valid values are 1 or +# greater (since 11.1) +# # @aio-max-batch: maximum number of requests in a batch for the AIO # engine, 0 means that the engine will use its default (since 6.1) # @@ -96,6 +101,7 @@ 'poll-max-ns': 'int', 'poll-grow': 'int', 'poll-shrink': 'int', + 'poll-weight': 'int', 'aio-max-batch': 'int' } } ## diff --git a/qapi/qom.json b/qapi/qom.json index c653248f85..dd45ac1087 100644 --- a/qapi/qom.json +++ b/qapi/qom.json @@ -606,6 +606,13 @@ # algorithm detects it is spending too long polling without # encountering events. 0 selects a default behaviour (default: 0) # +# @poll-weight: the weight factor for adaptive polling. Determines +# how much the most recent event interval affects the next +# polling duration calculation. If set to 0, the system default +# value of 3 is used. Typical values: 1 (high weight on recent +# interval), 2-4 (moderate weight on recent interval). +# (default: 0) (since 11.1) +# # The @aio-max-batch option is available since 6.1. # # Since: 2.0 @@ -614,7 +621,8 @@ 'base': 'EventLoopBaseProperties', 'data': { '*poll-max-ns': 'int', '*poll-grow': 'int', - '*poll-shrink': 'int' } } + '*poll-shrink': 'int', + '*poll-weight': 'int' } } ## # @MainLoopProperties: diff --git a/include/qemu/aio.h b/include/qemu/aio.h index 6c22064a28..e65e90093a 100644 --- a/include/qemu/aio.h +++ b/include/qemu/aio.h @@ -310,6 +310,7 @@ struct AioContext { int64_t poll_max_ns; /* maximum polling time in nanoseconds */ int64_t poll_grow; /* polling time growth factor */ int64_t poll_shrink; /* polling time shrink factor */ + int64_t poll_weight; /* weight of current interval in calculation */ /* AIO engine parameters */ int64_t aio_max_batch; /* maximum number of requests in a batch */ @@ -791,12 +792,13 @@ void aio_context_destroy(AioContext *ctx); * @max_ns: how long to busy poll for, in nanoseconds * @grow: polling time growth factor * @shrink: polling time shrink factor + * @weight: weight factor applied to the current polling interval * * Poll mode can be disabled by setting poll_max_ns to 0. */ void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns, int64_t grow, int64_t shrink, - Error **errp); + int64_t weight, Error **errp); /** * aio_context_set_aio_params: diff --git a/include/system/iothread.h b/include/system/iothread.h index e26d13c6c7..a1ef7696cb 100644 --- a/include/system/iothread.h +++ b/include/system/iothread.h @@ -21,6 +21,23 @@ #define TYPE_IOTHREAD "iothread" +#ifdef CONFIG_POSIX +/* + * Benchmark results from 2016 on NVMe SSD drives show max polling times around + * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32 + * workloads. + */ +#define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL +#define IOTHREAD_POLL_GROW_DEFAULT 2ULL +#define IOTHREAD_POLL_SHRINK_DEFAULT 2ULL +#define IOTHREAD_POLL_WEIGHT_DEFAULT 3ULL +#else +#define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL +#define IOTHREAD_POLL_GROW_DEFAULT 0ULL +#define IOTHREAD_POLL_SHRINK_DEFAULT 0ULL +#define IOTHREAD_POLL_WEIGHT_DEFAULT 0ULL +#endif + struct IOThread { EventLoopBase parent_obj; @@ -38,6 +55,7 @@ struct IOThread { int64_t poll_max_ns; int64_t poll_grow; int64_t poll_shrink; + int64_t poll_weight; }; typedef struct IOThread IOThread; diff --git a/iothread.c b/iothread.c index caf68e0764..3558535b40 100644 --- a/iothread.c +++ b/iothread.c @@ -25,17 +25,6 @@ #include "qemu/rcu.h" #include "qemu/main-loop.h" - -#ifdef CONFIG_POSIX -/* Benchmark results from 2016 on NVMe SSD drives show max polling times around - * 16-32 microseconds yield IOPS improvements for both iodepth=1 and iodepth=32 - * workloads. - */ -#define IOTHREAD_POLL_MAX_NS_DEFAULT 32768ULL -#else -#define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL -#endif - static void *iothread_run(void *opaque) { IOThread *iothread = opaque; @@ -103,6 +92,10 @@ static void iothread_instance_init(Object *obj) IOThread *iothread = IOTHREAD(obj); iothread->poll_max_ns = IOTHREAD_POLL_MAX_NS_DEFAULT; + iothread->poll_grow = IOTHREAD_POLL_GROW_DEFAULT; + iothread->poll_shrink = IOTHREAD_POLL_SHRINK_DEFAULT; + iothread->poll_weight = IOTHREAD_POLL_WEIGHT_DEFAULT; + iothread->thread_id = -1; qemu_sem_init(&iothread->init_done_sem, 0); /* By default, we don't run gcontext */ @@ -164,6 +157,7 @@ static void iothread_set_aio_context_params(EventLoopBase *base, Error **errp) iothread->poll_max_ns, iothread->poll_grow, iothread->poll_shrink, + iothread->poll_weight, errp); if (*errp) { return; @@ -233,6 +227,9 @@ static IOThreadParamInfo poll_grow_info = { static IOThreadParamInfo poll_shrink_info = { "poll-shrink", offsetof(IOThread, poll_shrink), }; +static IOThreadParamInfo poll_weight_info = { + "poll-weight", offsetof(IOThread, poll_weight), +}; static void iothread_get_param(Object *obj, Visitor *v, const char *name, IOThreadParamInfo *info, Error **errp) @@ -254,13 +251,31 @@ static bool iothread_set_param(Object *obj, Visitor *v, return false; } - if (value < 0) { + if (info->offset == offsetof(IOThread, poll_weight)) { + if (value < 0 || value > 63) { + error_setg(errp, "%s value must be in range [0, 63]", + info->name); + return false; + } + } else if (value < 0) { error_setg(errp, "%s value must be in range [0, %" PRId64 "]", info->name, INT64_MAX); return false; } - *field = value; + if (value == 0) { + if (info->offset == offsetof(IOThread, poll_grow)) { + *field = IOTHREAD_POLL_GROW_DEFAULT; + } else if (info->offset == offsetof(IOThread, poll_shrink)) { + *field = IOTHREAD_POLL_SHRINK_DEFAULT; + } else if (info->offset == offsetof(IOThread, poll_weight)) { + *field = IOTHREAD_POLL_WEIGHT_DEFAULT; + } else { + *field = value; + } + } else { + *field = value; + } return true; } @@ -288,6 +303,7 @@ static void iothread_set_poll_param(Object *obj, Visitor *v, iothread->poll_max_ns, iothread->poll_grow, iothread->poll_shrink, + iothread->poll_weight, errp); } } @@ -311,6 +327,10 @@ static void iothread_class_init(ObjectClass *klass, const void *class_data) iothread_get_poll_param, iothread_set_poll_param, NULL, &poll_shrink_info); + object_class_property_add(klass, "poll-weight", "int", + iothread_get_poll_param, + iothread_set_poll_param, + NULL, &poll_weight_info); } static const TypeInfo iothread_info = { @@ -356,6 +376,7 @@ static int query_one_iothread(Object *object, void *opaque) info->poll_max_ns = iothread->poll_max_ns; info->poll_grow = iothread->poll_grow; info->poll_shrink = iothread->poll_shrink; + info->poll_weight = iothread->poll_weight; info->aio_max_batch = iothread->parent_obj.aio_max_batch; QAPI_LIST_APPEND(*tail, info); diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c index bc26b39d70..afa7b709a6 100644 --- a/monitor/hmp-cmds.c +++ b/monitor/hmp-cmds.c @@ -206,6 +206,7 @@ void hmp_info_iothreads(Monitor *mon, const QDict *qdict) monitor_printf(mon, " poll-max-ns=%" PRId64 "\n", value->poll_max_ns); monitor_printf(mon, " poll-grow=%" PRId64 "\n", value->poll_grow); monitor_printf(mon, " poll-shrink=%" PRId64 "\n", value->poll_shrink); + monitor_printf(mon, " poll-weight=%" PRId64 "\n", value->poll_weight); monitor_printf(mon, " aio-max-batch=%" PRId64 "\n", value->aio_max_batch); } diff --git a/tests/unit/test-nested-aio-poll.c b/tests/unit/test-nested-aio-poll.c index 9ab1ad08a7..4c38f36fd4 100644 --- a/tests/unit/test-nested-aio-poll.c +++ b/tests/unit/test-nested-aio-poll.c @@ -81,7 +81,7 @@ static void test(void) qemu_set_current_aio_context(td.ctx); /* Enable polling */ - aio_context_set_poll_params(td.ctx, 1000000, 2, 2, &error_abort); + aio_context_set_poll_params(td.ctx, 1000000, 2, 2, 3, &error_abort); /* Make the event notifier active (set) right away */ event_notifier_init(&td.poll_notifier, 1); 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; diff --git a/qemu-options.hx b/qemu-options.hx index 21972f8326..29c09415c1 100644 --- a/qemu-options.hx +++ b/qemu-options.hx @@ -6443,7 +6443,7 @@ SRST CN=laptop.example.com,O=Example Home,L=London,ST=London,C=GB - ``-object iothread,id=id,poll-max-ns=poll-max-ns,poll-grow=poll-grow,poll-shrink=poll-shrink,aio-max-batch=aio-max-batch`` + ``-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`` Creates a dedicated event loop thread that devices can be assigned to. This is known as an IOThread. By default device emulation happens in vCPU threads or the main event loop thread. @@ -6479,6 +6479,12 @@ SRST the polling time when the algorithm detects it is spending too long polling without encountering events. + The ``poll-weight`` parameter is the weight factor for adaptive + polling. It determines how much the most recent event interval + affects the next polling duration calculation. If set to 0, the + system default value of 3 is used. Typical values: 1 (high weight + on recent interval), 2-4 (moderate weight on recent interval). + The ``aio-max-batch`` parameter is the maximum number of requests in a batch for the AIO engine, 0 means that the engine will use its default. -- 2.54.0
