From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 7A1AA106B53F for ; Wed, 25 Mar 2026 14:05:36 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1w5Oqa-000510-7e; Wed, 25 Mar 2026 10:04:36 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1w5OqY-00050G-H7 for qemu-devel@nongnu.org; Wed, 25 Mar 2026 10:04:34 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1w5OqU-0000wH-Ab for qemu-devel@nongnu.org; Wed, 25 Mar 2026 10:04:33 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1774447464; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=1R7mTulkhK8/TSM0U1Ck7YjzmrYxyDqutiTOYN/p0Xc=; b=ftUJSUkKNgmn6qOOoTAe1GnCfw88AuQovoqCTab6S5f6GFa18E42uoIFeRpwQlS4gJt+cj 2W3AQhg3KS+eC98dlKib7uvK871r7i15pMqQ/jJc72IOc8T+XLQKhRa+ZDuerdm3wN7f0t +OnpK/8sPXi4TsAbUSE13/eTnme0EJ4= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-584-jcHYMI8UN4G356iCIg7Z7Q-1; Wed, 25 Mar 2026 10:04:17 -0400 X-MC-Unique: jcHYMI8UN4G356iCIg7Z7Q-1 X-Mimecast-MFC-AGG-ID: jcHYMI8UN4G356iCIg7Z7Q_1774447455 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 3B767180049D; Wed, 25 Mar 2026 14:04:15 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.6]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B0D8419560B1; Wed, 25 Mar 2026 14:04:13 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 99D9B21E6937; Wed, 25 Mar 2026 15:04:10 +0100 (CET) From: Markus Armbruster To: Jaehoon Kim Cc: qemu-devel@nongnu.org, qemu-block@nongnu.org, mjrosato@linux.ibm.com, farman@linux.ibm.com, pbonzini@redhat.com, stefanha@redhat.com, fam@euphon.net, armbru@redhat.com, eblake@redhat.com, berrange@redhat.com, eduardo@habkost.net, dave@treblig.org, sw@weilnetz.de Subject: Re: [PATCH RFC v2 3/3] qapi/iothread: introduce poll-weight parameter for aio-poll In-Reply-To: <20260323135451.579655-4-jhkim@linux.ibm.com> (Jaehoon Kim's message of "Mon, 23 Mar 2026 08:54:51 -0500") References: <20260323135451.579655-1-jhkim@linux.ibm.com> <20260323135451.579655-4-jhkim@linux.ibm.com> Date: Wed, 25 Mar 2026 15:04:10 +0100 Message-ID: <87o6kckntx.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-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: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Jaehoon Kim writes: > 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 values for poll-grow > and poll-shrink parameters from the grow_polling_time() and > shrink_polling_time() functions, as these defaults are now properly > initialized in iothread.c during IOThread creation. > > Signed-off-by: Jaehoon Kim [...] > diff --git a/qapi/misc.json b/qapi/misc.json > index 28c641fe2f..39d17010bc 100644 > --- a/qapi/misc.json > +++ b/qapi/misc.json > @@ -85,6 +85,12 @@ Note: this is IOThreadInfo, used only as return value of query-iothreads. > # @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. 0 selects the system default value which is current 3 Does query-iothreads actually return 0? I'd expect it to return the value that is actually used. > +# (since 10.2) 11.1 most likely. > +# > # @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 +102,7 @@ > '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..feb80b6cfe 100644 > --- a/qapi/qom.json > +++ b/qapi/qom.json > @@ -606,6 +606,11 @@ > # 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 current event interval contributes to > +# the next polling time calculation. Valid values are 1 or > +# greater. If set to 0, the default value of 3 is used. The commit message hints what the valid values mean, the doc comment doesn't even that. Do users need to know? Code [*] below uses it like time >> poll_weight, where @time is int64_t. poll_weight > 63 is undefined behavior, which is a no-no. Please reject such values. poll_weight == 64 results in zero. Is that useful? Missing: (default: 0) (since 11.1) > +# > # The @aio-max-batch option is available since 6.1. > # > # Since: 2.0 > @@ -614,7 +619,8 @@ > 'base': 'EventLoopBaseProperties', > 'data': { '*poll-max-ns': 'int', > '*poll-grow': 'int', > - '*poll-shrink': 'int' } } > + '*poll-shrink': 'int', > + '*poll-weight': 'int' } } > > ## > # @MainLoopProperties: > diff --git a/qemu-options.hx b/qemu-options.hx > index 69e5a874c1..8ddf6c8d36 100644 > --- a/qemu-options.hx > +++ b/qemu-options.hx > @@ -6413,7 +6413,7 @@ 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. > @@ -6449,6 +6449,11 @@ 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 used in the > + adaptive polling algorithm. It determines how much the most > + recent event interval affects the calculation of the next > + polling duration. > + > 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. > 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 2b3522f2f9..13b7f94911 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 adjust_block_ns(AioContext *ctx, int64_t block_ns); > static void grow_polling_time(AioContext *ctx, int64_t block_ns); > @@ -593,10 +592,6 @@ static void shrink_polling_time(AioContext *ctx, int64_t block_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; > } > @@ -610,10 +605,6 @@ static void grow_polling_time(AioContext *ctx, int64_t block_ns) > 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 { > @@ -640,8 +631,8 @@ static void adjust_block_ns(AioContext *ctx, int64_t block_ns) > * poll.ns to smooth out polling time 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; [*] This is the use of @poll-weight referred to above. > > if (node->poll.ns > ctx->poll_max_ns) { > node->poll.ns = 0; > @@ -831,7 +822,8 @@ 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; > > @@ -848,6 +840,7 @@ void aio_context_set_poll_params(AioContext *ctx, int64_t max_ns, > ctx->poll_max_ns = max_ns; > ctx->poll_grow = grow; > ctx->poll_shrink = shrink; > + ctx->poll_weight = weight; > ctx->poll_ns = 0; > > aio_notify(ctx); [...]