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[80.230.34.155]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-43614cc4868sm4809896f8f.11.2026.02.03.07.52.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 03 Feb 2026 07:52:08 -0800 (PST) Date: Tue, 3 Feb 2026 10:52:06 -0500 From: "Michael S. Tsirkin" To: Manos Pitsidianakis Cc: Yanfeng Liu , kraxel@redhat.com, qemu-devel@nongnu.org, Yanfeng Liu Subject: Re: [PATCH v1] audio/virtio-snd: fix latency calc Message-ID: <20260203105150-mutt-send-email-mst@kernel.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Received-SPF: pass client-ip=170.10.133.124; envelope-from=mst@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_H2=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 On Sat, Nov 15, 2025 at 12:08:07PM +0200, Manos Pitsidianakis wrote: > On Fri, Nov 14, 2025 at 11:35 AM Yanfeng Liu wrote: > > > > Media players needs meaningful latency_bytes update but it is > > zero now most of the time. This adds stream-wise latency_bytes > > calculation so that to improve the situation. > > > > Signed-off-by: Yanfeng Liu > > --- Manos what do you want to do with this patch? > > Thanks for this patch. The virtio spec doesn't adequately explain what > latency_bytes means, could you explain what it does and why it's > needed? And also what behavior in media players this patch fixes? > > Thanks again! > > > hw/audio/virtio-snd.c | 12 +++++++++++- > > include/hw/audio/virtio-snd.h | 1 + > > 2 files changed, 12 insertions(+), 1 deletion(-) > > > > diff --git a/hw/audio/virtio-snd.c b/hw/audio/virtio-snd.c > > index 9101560f38..ed0422b45a 100644 > > --- a/hw/audio/virtio-snd.c > > +++ b/hw/audio/virtio-snd.c > > @@ -431,6 +431,7 @@ static uint32_t virtio_snd_pcm_prepare(VirtIOSound *s, uint32_t stream_id) > > stream->id = stream_id; > > stream->pcm = s->pcm; > > stream->s = s; > > + stream->latency_bytes = 0; > > qemu_mutex_init(&stream->queue_mutex); > > QSIMPLEQ_INIT(&stream->queue); > > > > @@ -899,6 +900,7 @@ static void virtio_snd_handle_tx_xfer(VirtIODevice *vdev, VirtQueue *vq) > > buffer->vq = vq; > > buffer->size = size; > > buffer->offset = 0; > > + stream->latency_bytes += size; > > > > QSIMPLEQ_INSERT_TAIL(&stream->queue, buffer, entry); > > } > > @@ -1112,12 +1114,19 @@ error_cleanup: > > virtio_snd_unrealize(dev); > > } > > > > +static inline void update_latency(VirtIOSoundPCMStream *s, size_t used) > > +{ > > + s->latency_bytes = s->latency_bytes > used ? > > + s->latency_bytes - used : 0; > > +} > > + > > static inline void return_tx_buffer(VirtIOSoundPCMStream *stream, > > VirtIOSoundPCMBuffer *buffer) > > { > > virtio_snd_pcm_status resp = { 0 }; > > resp.status = cpu_to_le32(VIRTIO_SND_S_OK); > > - resp.latency_bytes = cpu_to_le32((uint32_t)buffer->size); > > + update_latency(stream, buffer->size); > > + resp.latency_bytes = cpu_to_le32(stream->latency_bytes); > > iov_from_buf(buffer->elem->in_sg, > > buffer->elem->in_num, > > 0, > > @@ -1178,6 +1187,7 @@ static void virtio_snd_pcm_out_cb(void *data, int available) > > buffer->size -= size; > > buffer->offset += size; > > available -= size; > > + update_latency(stream, size); > > if (buffer->size < 1) { > > return_tx_buffer(stream, buffer); > > break; > > diff --git a/include/hw/audio/virtio-snd.h b/include/hw/audio/virtio-snd.h > > index c176066584..9560bac8b1 100644 > > --- a/include/hw/audio/virtio-snd.h > > +++ b/include/hw/audio/virtio-snd.h > > @@ -150,6 +150,7 @@ struct VirtIOSoundPCMStream { > > } voice; > > QemuMutex queue_mutex; > > bool active; > > + uint32_t latency_bytes; > > QSIMPLEQ_HEAD(, VirtIOSoundPCMBuffer) queue; > > }; > > > > -- > > 2.34.1 > >