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Tsirkin" , Takashi Iwai Cc: Jaroslav Kysela , linux-sound@vger.kernel.org, virtualization@lists.linux.dev, linux-kernel@vger.kernel.org Subject: [RFC PATCH 2/2] ALSA: virtio: prioritize staged capture period work Date: Sat, 17 Oct 2026 15:00:30 +0900 Message-ID: In-Reply-To: References: Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit CPU contention can delay staged capture period notifications while RX completions continue filling the unread ring. In a two-vCPU VZ guest with 16 nice-0 CPU workers, the ACK-fixed baseline stopped with ring_capacity and EPIPE in three runs, after 11.74, 30.77 and 30.33 seconds of audio. Route staged capture period work through system_highpri_wq with a common helper at all ten producers, including ACK errors and self-requeue. Keep playback and non-staged streams on the normal workqueue. Initialization, cancellation, buffer geometry and capture accounting remain unchanged. With the same kernel, input, geometry and userspace priority, the candidate completed three 70-second captures and immediate reopens. Its maximum matched queue-to-start delay was 20.366 ms, versus 108.112 ms in the first baseline failure. The other baseline failures had pending work without matching execution, so matched-only statistics do not bound that delay. Reader scheduling delays were also present. Both arms passed a separate nice -10 reader control, and host load varied between runs. These results support the change for the tested workload without isolating a kernel-only cause or guaranteeing lossless capture under arbitrary CPU load. KASAN/lockdep QEMU regressions passed with the unchanged candidate source. This follows the staged ACK fix and pending VZ capture support. The introducing staged-capture patch has no upstream Fixes commit ID yet. Link: https://lore.kernel.org/all/rfc-v2-vz-capture-compat-1.b9ab4c1540dc4691@gmail.com/ Assisted-by: LLM Signed-off-by: Joonho Lee --- sound/virtio/virtio_pcm.c | 4 ++-- sound/virtio/virtio_pcm.h | 12 ++++++++++++ sound/virtio/virtio_pcm_msg.c | 6 +++--- sound/virtio/virtio_pcm_ops.c | 10 +++++----- 4 files changed, 22 insertions(+), 10 deletions(-) diff --git a/sound/virtio/virtio_pcm.c b/sound/virtio/virtio_pcm.c index a3478fc8848db..d8515b2144a14 100644 --- a/sound/virtio/virtio_pcm.c +++ b/sound/virtio/virtio_pcm.c @@ -397,7 +397,7 @@ static void virtsnd_pcm_period_elapsed(struct work_struct *work) } if (requeue) - schedule_work(&vss->elapsed_period); + virtsnd_pcm_schedule_period_elapsed(vss); } /** @@ -606,7 +606,7 @@ void virtsnd_pcm_event(struct virtio_snd *snd, struct virtio_snd_event *event) if (vss->xfer_enabled) { vss->xfer_xrun = true; if (vss->capture_staging) - schedule_work(&vss->elapsed_period); + virtsnd_pcm_schedule_period_elapsed(vss); } } break; diff --git a/sound/virtio/virtio_pcm.h b/sound/virtio/virtio_pcm.h index e143a15592f05..5d1d88f2823b2 100644 --- a/sound/virtio/virtio_pcm.h +++ b/sound/virtio/virtio_pcm.h @@ -8,6 +8,7 @@ #include #include +#include #include #include @@ -114,6 +115,17 @@ struct virtio_pcm_substream { wait_queue_head_t msg_empty; }; +/* Keep non-staged PCM notifications on schedule_work()'s normal queue. */ +static inline bool +virtsnd_pcm_schedule_period_elapsed(struct virtio_pcm_substream *vss) +{ + if (vss->direction == SNDRV_PCM_STREAM_CAPTURE && + vss->capture_staging) + return queue_work(system_highpri_wq, &vss->elapsed_period); + + return schedule_work(&vss->elapsed_period); +} + /* * ALSA may observe a subperiod tail before its period callback. Keep actual * unread occupancy separate from pointer observations and notification state. diff --git a/sound/virtio/virtio_pcm_msg.c b/sound/virtio/virtio_pcm_msg.c index 795e52e09564b..663f7695b5be8 100644 --- a/sound/virtio/virtio_pcm_msg.c +++ b/sound/virtio/virtio_pcm_msg.c @@ -627,7 +627,7 @@ static void virtsnd_pcm_capture_xrun_locked(struct virtio_pcm_substream *vss) { if (!vss->xfer_xrun) { vss->xfer_xrun = true; - schedule_work(&vss->elapsed_period); + virtsnd_pcm_schedule_period_elapsed(vss); } } @@ -720,7 +720,7 @@ static void virtsnd_pcm_capture_complete(struct virtio_pcm_msg *msg, virtsnd_pcm_capture_xrun_locked(vss); } if (got_audio && !vss->xfer_xrun) - schedule_work(&vss->elapsed_period); + virtsnd_pcm_schedule_period_elapsed(vss); } else if (!vss->msg_count) { wake_up_all(&vss->msg_empty); } @@ -858,7 +858,7 @@ static void virtsnd_pcm_msg_complete(struct virtio_pcm_msg *msg, runtime->delay = bytes_to_frames(runtime, le32_to_cpu(msg->status.latency_bytes)); - schedule_work(&vss->elapsed_period); + virtsnd_pcm_schedule_period_elapsed(vss); } else if (!vss->msg_count) { wake_up_all(&vss->msg_empty); } diff --git a/sound/virtio/virtio_pcm_ops.c b/sound/virtio/virtio_pcm_ops.c index 85e7576903d56..d50924b792f65 100644 --- a/sound/virtio/virtio_pcm_ops.c +++ b/sound/virtio/virtio_pcm_ops.c @@ -232,7 +232,7 @@ virtsnd_pcm_pause_restart_fail(struct virtio_pcm_substream *vss, VIRTSND_PCM_PAUSE_RESTART_RESET_REQUIRED; } if (notify_xrun) - schedule_work(&vss->elapsed_period); + virtsnd_pcm_schedule_period_elapsed(vss); vss->substream->runtime->stop_operating = true; } @@ -1253,7 +1253,7 @@ static int virtsnd_pcm_capture_staged_ack(struct virtio_pcm_substream *vss, return -EPIPE; if (!virtsnd_pcm_capture_counters_valid(vss)) { vss->xfer_xrun = true; - schedule_work(&vss->elapsed_period); + virtsnd_pcm_schedule_period_elapsed(vss); return -EPIPE; } @@ -1264,7 +1264,7 @@ static int virtsnd_pcm_capture_staged_ack(struct virtio_pcm_substream *vss, if (diff < 0 || (snd_pcm_uframes_t)diff > runtime->buffer_size) { vss->xfer_xrun = true; - schedule_work(&vss->elapsed_period); + virtsnd_pcm_schedule_period_elapsed(vss); return -EPIPE; } @@ -1275,7 +1275,7 @@ static int virtsnd_pcm_capture_staged_ack(struct virtio_pcm_substream *vss, &next_acked_total) || next_acked_total > vss->capture_copied_total) { vss->xfer_xrun = true; - schedule_work(&vss->elapsed_period); + virtsnd_pcm_schedule_period_elapsed(vss); return -EPIPE; } @@ -1292,7 +1292,7 @@ static int virtsnd_pcm_capture_staged_ack(struct virtio_pcm_substream *vss, rc = virtsnd_pcm_capture_send(vss); if (rc) { vss->xfer_xrun = true; - schedule_work(&vss->elapsed_period); + virtsnd_pcm_schedule_period_elapsed(vss); } } }