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 EB0ABC3ABC3 for ; Sat, 10 May 2025 15:03:52 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uDljA-0003Zf-2b; Sat, 10 May 2025 11:03:00 -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 1uDlj7-0003ZP-6Y for qemu-devel@nongnu.org; Sat, 10 May 2025 11:02:57 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uDlj3-0006lb-Pb for qemu-devel@nongnu.org; Sat, 10 May 2025 11:02:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1746889369; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=YdCpAelFZ594j6QduP0suf0lYGyWqFqixFvIcyZiHqo=; b=QKCF0Gxlgb/KG7K1d1Bb4Rlut3D+UrFATJ5x/eQoA0hG/BAU0BXzfC+M0F6+LJEdaebM5O y+SISzUJY2tJC5rpx9205o+zDd8Dc4iIypICbQpT/dQFQwFnC2IuKDvSeLTHooyZvjqzuV TKxAPv1DycTQvLfVqNbIKm86wdHNElY= Received: from mail-ej1-f71.google.com (mail-ej1-f71.google.com [209.85.218.71]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-255-pArkIyNkNBiVpNhd9aZNBg-1; Sat, 10 May 2025 11:02:47 -0400 X-MC-Unique: pArkIyNkNBiVpNhd9aZNBg-1 X-Mimecast-MFC-AGG-ID: pArkIyNkNBiVpNhd9aZNBg_1746889367 Received: by mail-ej1-f71.google.com with SMTP id a640c23a62f3a-ad2363a3949so79675566b.0 for ; Sat, 10 May 2025 08:02:47 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1746889366; x=1747494166; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=YdCpAelFZ594j6QduP0suf0lYGyWqFqixFvIcyZiHqo=; b=rpYhAb+37dwpfZQLTaZCTAvDqu542mRZSdA1y3At/aCcWWEB7s1gtvrvenorl7x0Ha qGz0qaz/psQ0O3wSYaskHtAFP6XBWw2uK5O8cjwINZj651mPbR0BmmcXYOn6ZXb7uhNd Tr/DwuV4QV7LMlPn+wCOIPJmkLOMCId7VUj0LoM4rqaTrr0dcIztKuq6vLwFH+c9m5wz /bVbHdzcyXRFmbFiOOMFncPJqPxfZnEPI0LN5f7b8e2Q6ETBI5RQmmoRC23cBY6G2uuX 52ILYIqanKOxuuXS1xOqrpHVUY/7OJX2M5l7zWrCXZ9SXZdSMZmmSDbNarnnHEoRk3qX 8j9w== X-Forwarded-Encrypted: i=1; AJvYcCURn7QkLqedVfJgcoxAq5UWgbg3/+DAAnehcqjALTxosx0wKpFeIo8kcIoCVxt6HCvqclK/j+A9l1kU@nongnu.org X-Gm-Message-State: AOJu0Ywpyj6DZGbQUgkadNK1FgtTeiHDkw7DeHZEuZ5etEnGZceXB0SS 5GWoxTRQlFpF9GDvR+gPUdj+/5xbdwe9cx0dJjXgoAUgUaPLsBcE+JevPQmjaKcrU5qplm9MFeL RaG/0QelBtghJz1cEdPncL3NgOTBUCjQU7vYmAOj1jQtYI7xXAwMn X-Gm-Gg: ASbGnctUOgeXaTx9BY3NBFPQBEsuLu6Tlt1mXhgJ2DIvAxuYjOIGvOt1i8sxGqyiDTv 3flqIm6ABzQklFnFUkXNi086CqasDYYqqKlZo6gA+ziQ9v1n4XWz1KF830GRGXVJ4SpH747eifN 9kYVKhZc2PCWzjYSN/12T9JUrdKAhMA+TePx/RM6GXzylm3KzBCaDq+zRyog5sw1naVYe4DuTAy 39/xmkuju89qV6bHvXkxTRDP7NB+GwYKUSMoUnYxjvKef+J16REbuMPAeeTuz0YFTrZn427arir GOtDxnCwgjJMIrg= X-Received: by 2002:a05:6402:5187:b0:5f5:6299:ad68 with SMTP id 4fb4d7f45d1cf-5fca0759ac0mr6111378a12.11.1746889366538; Sat, 10 May 2025 08:02:46 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEAIsLNPS0nHo4JAa1vEtIBp26NrF9J5Ag64/7/to8LTtY8rybpcII9IHTxeO8wKYsN8wbhQg== X-Received: by 2002:a05:6402:5187:b0:5f5:6299:ad68 with SMTP id 4fb4d7f45d1cf-5fca0759ac0mr6111327a12.11.1746889366033; Sat, 10 May 2025 08:02:46 -0700 (PDT) Received: from [192.168.10.48] ([151.62.197.53]) by smtp.googlemail.com with ESMTPSA id 4fb4d7f45d1cf-5fc9cbe516asm2988741a12.15.2025.05.10.08.02.44 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sat, 10 May 2025 08:02:45 -0700 (PDT) Message-ID: <54bb98a7-110d-41d2-a683-1428cb7d94a2@redhat.com> Date: Sat, 10 May 2025 17:02:42 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/9] qemu-thread: Avoid futex abstraction for non-Linux To: Akihiko Odaki , Stefan Weil , Peter Xu , Fabiano Rosas , Hailiang Zhang Cc: Phil Dennis-Jordan , qemu-devel@nongnu.org, devel@daynix.com, =?UTF-8?Q?Marc-Andr=C3=A9_Lureau?= , =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= , =?UTF-8?Q?Philippe_Mathieu-Daud=C3=A9?= References: <20250510-event-v2-0-7953177ce1b8@daynix.com> <20250510-event-v2-3-7953177ce1b8@daynix.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; keydata= xsEhBFRCcBIBDqDGsz4K0zZun3jh+U6Z9wNGLKQ0kSFyjN38gMqU1SfP+TUNQepFHb/Gc0E2 CxXPkIBTvYY+ZPkoTh5xF9oS1jqI8iRLzouzF8yXs3QjQIZ2SfuCxSVwlV65jotcjD2FTN04 hVopm9llFijNZpVIOGUTqzM4U55sdsCcZUluWM6x4HSOdw5F5Utxfp1wOjD/v92Lrax0hjiX DResHSt48q+8FrZzY+AUbkUS+Jm34qjswdrgsC5uxeVcLkBgWLmov2kMaMROT0YmFY6A3m1S P/kXmHDXxhe23gKb3dgwxUTpENDBGcfEzrzilWueOeUWiOcWuFOed/C3SyijBx3Av/lbCsHU Vx6pMycNTdzU1BuAroB+Y3mNEuW56Yd44jlInzG2UOwt9XjjdKkJZ1g0P9dwptwLEgTEd3Fo UdhAQyRXGYO8oROiuh+RZ1lXp6AQ4ZjoyH8WLfTLf5g1EKCTc4C1sy1vQSdzIRu3rBIjAvnC tGZADei1IExLqB3uzXKzZ1BZ+Z8hnt2og9hb7H0y8diYfEk2w3R7wEr+Ehk5NQsT2MPI2QBd wEv1/Aj1DgUHZAHzG1QN9S8wNWQ6K9DqHZTBnI1hUlkp22zCSHK/6FwUCuYp1zcAEQEAAc0j UGFvbG8gQm9uemluaSA8cGJvbnppbmlAcmVkaGF0LmNvbT7CwU0EEwECACMFAlRCcBICGwMH CwkIBwMCAQYVCAIJCgsEFgIDAQIeAQIXgAAKCRB+FRAMzTZpsbceDp9IIN6BIA0Ol7MoB15E 11kRz/ewzryFY54tQlMnd4xxfH8MTQ/mm9I482YoSwPMdcWFAKnUX6Yo30tbLiNB8hzaHeRj jx12K+ptqYbg+cevgOtbLAlL9kNgLLcsGqC2829jBCUTVeMSZDrzS97ole/YEez2qFpPnTV0 VrRWClWVfYh+JfzpXmgyhbkuwUxNFk421s4Ajp3d8nPPFUGgBG5HOxzkAm7xb1cjAuJ+oi/K CHfkuN+fLZl/u3E/fw7vvOESApLU5o0icVXeakfSz0LsygEnekDbxPnE5af/9FEkXJD5EoYG SEahaEtgNrR4qsyxyAGYgZlS70vkSSYJ+iT2rrwEiDlo31MzRo6Ba2FfHBSJ7lcYdPT7bbk9 AO3hlNMhNdUhoQv7M5HsnqZ6unvSHOKmReNaS9egAGdRN0/GPDWr9wroyJ65ZNQsHl9nXBqE AukZNr5oJO5vxrYiAuuTSd6UI/xFkjtkzltG3mw5ao2bBpk/V/YuePrJsnPFHG7NhizrxttB nTuOSCMo45pfHQ+XYd5K1+Cv/NzZFNWscm5htJ0HznY+oOsZvHTyGz3v91pn51dkRYN0otqr bQ4tlFFuVjArBZcapSIe6NV8C4cEiSTOwE0EVEJx7gEIAMeHcVzuv2bp9HlWDp6+RkZe+vtl KwAHplb/WH59j2wyG8V6i33+6MlSSJMOFnYUCCL77bucx9uImI5nX24PIlqT+zasVEEVGSRF m8dgkcJDB7Tps0IkNrUi4yof3B3shR+vMY3i3Ip0e41zKx0CvlAhMOo6otaHmcxr35sWq1Jk tLkbn3wG+fPQCVudJJECvVQ//UAthSSEklA50QtD2sBkmQ14ZryEyTHQ+E42K3j2IUmOLriF dNr9NvE1QGmGyIcbw2NIVEBOK/GWxkS5+dmxM2iD4Jdaf2nSn3jlHjEXoPwpMs0KZsgdU0pP JQzMUMwmB1wM8JxovFlPYrhNT9MAEQEAAcLBMwQYAQIACQUCVEJx7gIbDAAKCRB+FRAMzTZp sadRDqCctLmYICZu4GSnie4lKXl+HqlLanpVMOoFNnWs9oRP47MbE2wv8OaYh5pNR9VVgyhD OG0AU7oidG36OeUlrFDTfnPYYSF/mPCxHttosyt8O5kabxnIPv2URuAxDByz+iVbL+RjKaGM GDph56ZTswlx75nZVtIukqzLAQ5fa8OALSGum0cFi4ptZUOhDNz1onz61klD6z3MODi0sBZN Aj6guB2L/+2ZwElZEeRBERRd/uommlYuToAXfNRdUwrwl9gRMiA0WSyTb190zneRRDfpSK5d usXnM/O+kr3Dm+Ui+UioPf6wgbn3T0o6I5BhVhs4h4hWmIW7iNhPjX1iybXfmb1gAFfjtHfL xRUr64svXpyfJMScIQtBAm0ihWPltXkyITA92ngCmPdHa6M1hMh4RDX+Jf1fiWubzp1voAg0 JBrdmNZSQDz0iKmSrx8xkoXYfA3bgtFN8WJH2xgFL28XnqY4M6dLhJwV3z08tPSRqYFm4NMP dRsn0/7oymhneL8RthIvjDDQ5ktUjMe8LtHr70OZE/TT88qvEdhiIVUogHdo4qBrk41+gGQh b906Dudw5YhTJFU3nC6bbF2nrLlB4C/XSiH76ZvqzV0Z/cAMBo5NF/w= In-Reply-To: <20250510-event-v2-3-7953177ce1b8@daynix.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -34 X-Spam_score: -3.5 X-Spam_bar: --- X-Spam_report: (-3.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1.413, 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_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, 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: 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 On 5/10/25 10:51, Akihiko Odaki wrote: > Add special implementations of qemu_event_set() and qemu_event_wait() > using pthread primitives. qemu_event_wait() will ensure qemu_event_set() > finishes, and these functions will avoid complex barrier and atomic > operations. Unfortunately not... > Signed-off-by: Akihiko Odaki > Tested-by: Phil Dennis-Jordan > Reviewed-by: Phil Dennis-Jordan > --- > util/qemu-thread-posix.c | 45 ++++++++++++++++++--------------------------- > 1 file changed, 18 insertions(+), 27 deletions(-) > > diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c > index 13459e44c768..805cac444f15 100644 > --- a/util/qemu-thread-posix.c > +++ b/util/qemu-thread-posix.c > @@ -319,28 +319,6 @@ void qemu_sem_wait(QemuSemaphore *sem) > > #ifdef __linux__ > #include "qemu/futex.h" > -#else > -static inline void qemu_futex_wake(QemuEvent *ev, int n) > -{ > - assert(ev->initialized); > - pthread_mutex_lock(&ev->lock); > - if (n == 1) { > - pthread_cond_signal(&ev->cond); > - } else { > - pthread_cond_broadcast(&ev->cond); > - } > - pthread_mutex_unlock(&ev->lock); > -} > - > -static inline void qemu_futex_wait(QemuEvent *ev, unsigned val) > -{ > - assert(ev->initialized); > - pthread_mutex_lock(&ev->lock); > - if (ev->value == val) { > - pthread_cond_wait(&ev->cond, &ev->lock); > - } > - pthread_mutex_unlock(&ev->lock); > -} > #endif > > /* Valid transitions: > @@ -363,7 +341,7 @@ static inline void qemu_futex_wait(QemuEvent *ev, unsigned val) > > void qemu_event_init(QemuEvent *ev, bool init) > { > -#ifndef __linux__ > +#ifndef CONFIG_LINUX > pthread_mutex_init(&ev->lock, NULL); > pthread_cond_init(&ev->cond, NULL); > #endif > @@ -376,7 +354,7 @@ void qemu_event_destroy(QemuEvent *ev) > { > assert(ev->initialized); > ev->initialized = false; > -#ifndef __linux__ > +#ifndef CONFIG_LINUX > pthread_mutex_destroy(&ev->lock); > pthread_cond_destroy(&ev->cond); > #endif > @@ -386,6 +364,7 @@ void qemu_event_set(QemuEvent *ev) > { > assert(ev->initialized); > > +#ifdef CONFIG_LINUX > /* > * Pairs with both qemu_event_reset() and qemu_event_wait(). > * The user of this code will not have mutexes so some care is needed. You have: if (!qatomic_load_acquire(&done)) { qemu_event_reset(&ev); if (!qatomic_load_acquire(&done)) qemu_event_wait(&ev); } and on the other side qatomic_store_release(&done, 1); qemu_event_set(&ev); --> qatomic_set(&ev.value, EV_SET); I don't think this is correct without the memory barrier in qemu_event_set(), though I am not actually sure how you'd add it. The problem is, I don't see anything that prevents this: set done qemu_event_set() pthread_mutex_lock() ev.value = SET qemu_event_reset() ev.value |= FREE smp_mb__after_rmw() // store buffer not flushed yet, // so other thread doesn't see "done" read done pthread_mutex_lock() pthread_cond_broadcast() pthread_mutex_unlock() while ev.value != SET // hang pthread_cond_wait() The barrier in qemu_event_reset() is not enough, you need one on each side. > +#else > + pthread_mutex_lock(&ev->lock); > + if (qatomic_read(&ev->value) != EV_SET) { Apart from the above this needs to be a while(), because condition variables also have spurious wakeups. Paolo > + pthread_cond_wait(&ev->cond, &ev->lock); > + } > + pthread_mutex_unlock(&ev->lock); > +#endif > } > > static __thread NotifierList thread_exit; >