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c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1753390036; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=rbYs+8k6eVMUp1Wr8L7PFzngQ03/Wf+JnHjPQ19gOec=; b=SjHO0hku3IM7PgAev8ASI+2jI4Cs55o2b/x3rDQzulWlFoTIRi6y1m3LXnrsZTqnAYdqL0 zubdTWl0IpvdgRHR6i/FeEFC8mLLmknbk6k5fBKVAqCBg/+nn6ldkdsEWI2Apjqa1Vbm39 FBREwQ5bcPrZtqp+FaSitfIhX9VHxW8= X-MC-Unique: 4DwYgUKeNzODL8yqGn8pVw-1 X-Mimecast-MFC-AGG-ID: 4DwYgUKeNzODL8yqGn8pVw_1753390028 From: Stefan Hajnoczi To: qemu-devel@nongnu.org Cc: Stefan Hajnoczi , Brian Song , qemu-block@nongnu.org, Bernd Schubert , Kevin Wolf , h0lyalg0rithm@git.sr.ht, Fam Zheng Subject: [RFC 1/3] iothread: create AioContext in iothread_run() Date: Thu, 24 Jul 2025 16:47:00 -0400 Message-ID: <20250724204702.576637-2-stefanha@redhat.com> In-Reply-To: <20250724204702.576637-1-stefanha@redhat.com> References: <20250724204702.576637-1-stefanha@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" The IOThread's AioContext is currently created in iothread_init() where it's easy to propagate errors before spawning the thread that runs iothread_run(). However, this means that aio_context_new() is called from the main loop thread rather than from the IOThread. In order to use Linux io_uring's IORING_SETUP_SINGLE_ISSUER feature in the next commit, only one thread can use the io_uring context and therefore iothread.c must call aio_context_new() from iothread_run() instead of iothread_init(). Extract the iothread_run() arguments into an IOThreadRunArgs struct where an Error *error field can be used to report back initialization errors. This works pretty well thanks to the init_done_sem semaphore that is already used by iothread_init() to wait for iothread_run() to initialize. Move iothread_run() further down for proximity with iothread_init() and to avoid adding a function prototype for iothread_set_aio_context_params(). Signed-off-by: Stefan Hajnoczi --- include/system/iothread.h | 1 - iothread.c | 140 +++++++++++++++++++++----------------- 2 files changed, 78 insertions(+), 63 deletions(-) diff --git a/include/system/iothread.h b/include/system/iothread.h index d95c17a645..ec4e798d5e 100644 --- a/include/system/iothread.h +++ b/include/system/iothread.h @@ -29,7 +29,6 @@ struct IOThread { bool run_gcontext; /* whether we should run gcontext */ GMainContext *worker_context; GMainLoop *main_loop; - QemuSemaphore init_done_sem; /* is thread init done? */ bool stopping; /* has iothread_stop() been called? */ bool running; /* should iothread_run() continue? */ int thread_id; diff --git a/iothread.c b/iothread.c index 8810376dce..c6547779d0 100644 --- a/iothread.c +++ b/iothread.c @@ -36,46 +36,6 @@ #define IOTHREAD_POLL_MAX_NS_DEFAULT 0ULL #endif =20 -static void *iothread_run(void *opaque) -{ - IOThread *iothread =3D opaque; - - rcu_register_thread(); - /* - * g_main_context_push_thread_default() must be called before anything - * in this new thread uses glib. - */ - g_main_context_push_thread_default(iothread->worker_context); - qemu_set_current_aio_context(iothread->ctx); - iothread->thread_id =3D qemu_get_thread_id(); - qemu_sem_post(&iothread->init_done_sem); - - while (iothread->running) { - /* - * Note: from functional-wise the g_main_loop_run() below can - * already cover the aio_poll() events, but we can't run the - * main loop unconditionally because explicit aio_poll() here - * is faster than g_main_loop_run() when we do not need the - * gcontext at all (e.g., pure block layer iothreads). In - * other words, when we want to run the gcontext with the - * iothread we need to pay some performance for functionality. - */ - aio_poll(iothread->ctx, true); - - /* - * We must check the running state again in case it was - * changed in previous aio_poll() - */ - if (iothread->running && qatomic_read(&iothread->run_gcontext)) { - g_main_loop_run(iothread->main_loop); - } - } - - g_main_context_pop_thread_default(iothread->worker_context); - rcu_unregister_thread(); - return NULL; -} - /* Runs in iothread_run() thread */ static void iothread_stop_bh(void *opaque) { @@ -104,7 +64,6 @@ static void iothread_instance_init(Object *obj) =20 iothread->poll_max_ns =3D IOTHREAD_POLL_MAX_NS_DEFAULT; iothread->thread_id =3D -1; - qemu_sem_init(&iothread->init_done_sem, 0); /* By default, we don't run gcontext */ qatomic_set(&iothread->run_gcontext, 0); } @@ -135,7 +94,6 @@ static void iothread_instance_finalize(Object *obj) g_main_loop_unref(iothread->main_loop); iothread->main_loop =3D NULL; } - qemu_sem_destroy(&iothread->init_done_sem); } =20 static void iothread_init_gcontext(IOThread *iothread, const char *thread_= name) @@ -176,47 +134,105 @@ static void iothread_set_aio_context_params(EventLoo= pBase *base, Error **errp) base->thread_pool_max, errp); } =20 +typedef struct { + IOThread *iothread; + const char *thread_name; + QemuSemaphore init_done_sem; /* is thread init done? */ + Error *error; /* filled in before init_done_sem is posted */ +} IOThreadRunArgs; =20 -static void iothread_init(EventLoopBase *base, Error **errp) +static void *iothread_run(void *opaque) { - Error *local_error =3D NULL; - IOThread *iothread =3D IOTHREAD(base); - g_autofree char *thread_name =3D NULL; + IOThreadRunArgs *args =3D opaque; + IOThread *iothread =3D args->iothread; =20 - iothread->stopping =3D false; - iothread->running =3D true; - iothread->ctx =3D aio_context_new(errp); + rcu_register_thread(); + + iothread->ctx =3D aio_context_new(&args->error); if (!iothread->ctx) { - return; + goto out; } =20 - thread_name =3D g_strdup_printf("IO %s", - object_get_canonical_path_component(OBJECT(base))); + iothread_set_aio_context_params(EVENT_LOOP_BASE(iothread), &args->erro= r); + if (args->error) { + aio_context_unref(iothread->ctx); + iothread->ctx =3D NULL; + goto out; + } =20 /* * Init one GMainContext for the iothread unconditionally, even if * it's not used */ - iothread_init_gcontext(iothread, thread_name); + iothread_init_gcontext(iothread, args->thread_name); =20 - iothread_set_aio_context_params(base, &local_error); - if (local_error) { - error_propagate(errp, local_error); - aio_context_unref(iothread->ctx); - iothread->ctx =3D NULL; - return; + /* + * g_main_context_push_thread_default() must be called before anything + * in this new thread uses glib. + */ + g_main_context_push_thread_default(iothread->worker_context); + qemu_set_current_aio_context(iothread->ctx); + + iothread->stopping =3D false; + iothread->running =3D true; + + iothread->thread_id =3D qemu_get_thread_id(); + qemu_sem_post(&args->init_done_sem); + + while (iothread->running) { + /* + * Note: from functional-wise the g_main_loop_run() below can + * already cover the aio_poll() events, but we can't run the + * main loop unconditionally because explicit aio_poll() here + * is faster than g_main_loop_run() when we do not need the + * gcontext at all (e.g., pure block layer iothreads). In + * other words, when we want to run the gcontext with the + * iothread we need to pay some performance for functionality. + */ + aio_poll(iothread->ctx, true); + + /* + * We must check the running state again in case it was + * changed in previous aio_poll() + */ + if (iothread->running && qatomic_read(&iothread->run_gcontext)) { + g_main_loop_run(iothread->main_loop); + } } =20 + g_main_context_pop_thread_default(iothread->worker_context); +out: + rcu_unregister_thread(); + return NULL; +} + +static void iothread_init(EventLoopBase *base, Error **errp) +{ + IOThread *iothread =3D IOTHREAD(base); + g_autofree char *thread_name =3D NULL; + IOThreadRunArgs args =3D { + .iothread =3D iothread, + }; + + qemu_sem_init(&args.init_done_sem, 0); + + thread_name =3D g_strdup_printf("IO %s", + object_get_canonical_path_component(OBJECT(base))); + args.thread_name =3D thread_name; + /* This assumes we are called from a thread with useful CPU affinity f= or us * to inherit. */ - qemu_thread_create(&iothread->thread, thread_name, iothread_run, - iothread, QEMU_THREAD_JOINABLE); + qemu_thread_create(&iothread->thread, thread_name, iothread_run, &args, + QEMU_THREAD_JOINABLE); =20 /* Wait for initialization to complete */ while (iothread->thread_id =3D=3D -1) { - qemu_sem_wait(&iothread->init_done_sem); + qemu_sem_wait(&args.init_done_sem); } + + qemu_sem_destroy(&args.init_done_sem); + error_propagate(errp, args.error); } =20 typedef struct { --=20 2.50.1