[FFmpeg-devel] [PATCH 07/16] hwcontext_nvtegra: add dynamic frequency scaling routines

[averne <averne381@gmail.com>]

To save on energy, the clock speed of multimedia engines should be adapted to their workload.

Signed-off-by: averne <averne381@gmail.com>
---
 libavutil/hwcontext_nvtegra.c | 165 ++++++++++++++++++++++++++++++++++
 libavutil/hwcontext_nvtegra.h |   7 ++
 2 files changed, 172 insertions(+)

diff --git a/libavutil/hwcontext_nvtegra.c b/libavutil/hwcontext_nvtegra.c
index 0f4d5a323b..6b72348082 100644
--- a/libavutil/hwcontext_nvtegra.c
+++ b/libavutil/hwcontext_nvtegra.c
@@ -46,6 +46,14 @@ typedef struct NVTegraDevicePriv {
 
     AVNVTegraJobPool job_pool;
     uint32_t vic_setup_off, vic_cmdbuf_off;
+
+    double framerate;
+    uint32_t dfs_lowcorner;
+    double dfs_decode_cycles_ema;
+    double dfs_ema_damping;
+    int dfs_bitrate_sum;
+    int dfs_cur_sample, dfs_num_samples;
+    int64_t dfs_sampling_start_ts, dfs_last_ts_delta;
 } NVTegraDevicePriv;
 
 static const enum AVPixelFormat supported_sw_formats[] = {
@@ -108,6 +116,28 @@ static inline uint32_t nvtegra_surface_get_height_align(enum AVPixelFormat fmt,
     return 32;
 }
 
+static int nvtegra_channel_set_freq(AVNVTegraChannel *channel, uint32_t freq) {
+    int err;
+#ifndef __SWITCH__
+    err = av_nvtegra_channel_set_clock_rate(channel, channel->module_id, freq);
+    if (err < 0)
+        return err;
+
+    err = av_nvtegra_channel_get_clock_rate(channel, channel->module_id, &channel->clock);
+    if (err < 0)
+        return err;
+#else
+    err = AVERROR(mmuRequestSetAndWait(&channel->mmu_request, freq, -1));
+    if (err < 0)
+        return err;
+
+    err = AVERROR(mmuRequestGet(&channel->mmu_request, &channel->clock));
+    if (err < 0)
+        return err;
+#endif
+    return 0;
+}
+
 static void nvtegra_device_uninit(AVHWDeviceContext *ctx) {
     NVTegraDevicePriv       *priv = ctx->hwctx;
     AVNVTegraDeviceContext *hwctx = &priv->p;
@@ -386,6 +416,141 @@ static int nvtegra_get_buffer(AVHWFramesContext *ctx, AVFrame *frame) {
     return 0;
 }
 
+/*
+ * Possible frequencies on Icosa and Mariko+, in MHz
+ * (see tegra210-core-dvfs.c and tegra210b01-core-dvfs.c in l4t kernel sources, respectively):
+ * for NVDEC:
+ *   268.8, 384.0, 448.0, 486.4, 550.4, 576.0, 614.4, 652.8, 678.4, 691.2, 716.8
+ *   460.8, 499.2, 556.8, 633.6, 652.8, 710.4, 748.8, 787.2, 825.6, 844.8, 883.2, 902.4, 921.6, 940.8, 960.0, 979.2
+ * for NVJPG:
+ *   192.0, 307.2, 345.6, 409.6, 486.4, 524.8, 550.4, 576.0, 588.8, 614.4, 627.2
+ *   422.4, 441.6, 499.2, 518.4, 537.6, 556.8, 576.0, 595.2, 614.4, 633.6, 652.8
+ */
+
+int av_nvtegra_dfs_init(AVHWDeviceContext *ctx, AVNVTegraChannel *channel, int width, int height,
+                        double framerate_hz)
+{
+    NVTegraDevicePriv *priv = ctx->hwctx;
+
+    uint32_t max_freq, lowcorner;
+    int num_mbs, err;
+
+    priv->dfs_num_samples = 20;
+    priv->dfs_ema_damping = 0.1;
+
+    /*
+     * Initialize low-corner frequency (reproduces official code)
+     * Framerate might be unavailable (or variable), but this is official logic
+     */
+    num_mbs = width / 16 * height / 16;
+    if (num_mbs <= 3600)
+        lowcorner = 100000000;  /* 480p */
+    else if (num_mbs <= 8160)
+        lowcorner = 180000000;  /* 720p */
+    else if (num_mbs <= 32400)
+        lowcorner = 345000000;  /* 1080p */
+    else
+        lowcorner = 576000000;  /* 4k */
+
+    if (framerate_hz >= 0.1 && isfinite(framerate_hz))
+        lowcorner = FFMIN(lowcorner, lowcorner * framerate_hz / 30.0);
+
+    priv->framerate     = framerate_hz;
+    priv->dfs_lowcorner = lowcorner;
+
+    av_log(ctx, AV_LOG_DEBUG, "DFS: Initializing lowcorner to %d Hz, using %u samples\n",
+           priv->dfs_lowcorner, priv->dfs_num_samples);
+
+    /*
+     * Initialize channel to the max possible frequency (the kernel driver will clamp to an allowed value)
+     * Note: Official code passes INT_MAX kHz then multiplies by 1000 (to Hz) and converts to u32,
+     * resulting in this value.
+     */
+    max_freq = (UINT64_C(1)<<32) - 1000 & UINT32_MAX;
+
+    err = nvtegra_channel_set_freq(channel, max_freq);
+    if (err < 0)
+        return err;
+
+    priv->dfs_decode_cycles_ema = 0.0;
+    priv->dfs_bitrate_sum       = 0;
+    priv->dfs_cur_sample        = 0;
+    priv->dfs_sampling_start_ts = av_gettime_relative();
+    priv->dfs_last_ts_delta     = 0;
+
+    return 0;
+}
+
+int av_nvtegra_dfs_update(AVHWDeviceContext *ctx, AVNVTegraChannel *channel, int bitstream_len, int decode_cycles) {
+    NVTegraDevicePriv *priv = ctx->hwctx;
+
+    double frame_time, avg;
+    int64_t now, wl_dt;
+    uint32_t clock;
+    int err;
+
+    /*
+     * Official software implements DFS using a flat average of the decoder pool occupancy.
+     * We instead use the decode cycles as reported by NVDEC microcode, and the "bitrate"
+     * (bitstream bits fed to the hardware in a given clock time interval, NOT video time),
+     * to calculate a suitable frequency, and multiply it by 1.2 for good measure:
+     *   Freq = decode_cycles_per_bit * bits_per_second * 1.2
+     */
+
+    /* Convert to bits */
+    bitstream_len *= 8;
+
+    /* Exponential moving average of decode cycles per frame */
+    priv->dfs_decode_cycles_ema = priv->dfs_ema_damping * (double)decode_cycles/bitstream_len +
+        (1.0 - priv->dfs_ema_damping) * priv->dfs_decode_cycles_ema;
+
+    priv->dfs_bitrate_sum += bitstream_len;
+    priv->dfs_cur_sample   = (priv->dfs_cur_sample + 1) % priv->dfs_num_samples;
+
+    err = 0;
+
+    /* Reclock if we collected enough samples */
+    if (priv->dfs_cur_sample == 0) {
+        now   = av_gettime_relative();
+        wl_dt = now - priv->dfs_sampling_start_ts;
+
+        /*
+         * Try to filter bad sample sets caused by eg. pausing the video playback.
+         * We reject if one of these conditions is met:
+         * - the wall time is over 1.5x the framerate (10Hz is used as fallback if no framerate information is available)
+         * - the wall time is over 1.5x the ema-damped previous values
+         */
+
+        if (priv->framerate >= 0.1 && isfinite(priv->framerate))
+            frame_time = 1.0e6 / priv->framerate;
+        else
+            frame_time = 0.1e6;
+
+        if ((wl_dt < 1.5 * priv->dfs_num_samples * frame_time) ||
+                ((priv->dfs_last_ts_delta) && (wl_dt < 1.5 * priv->dfs_last_ts_delta))) {
+            avg   = priv->dfs_bitrate_sum * 1e6 / wl_dt;
+            clock = priv->dfs_decode_cycles_ema * avg * 1.2;
+            clock = FFMAX(clock, priv->dfs_lowcorner);
+
+            av_log(ctx, AV_LOG_DEBUG, "DFS: %.0f cycles/b (ema), %.0f b/s -> clock %u Hz (lowcorner %u Hz)\n",
+                priv->dfs_decode_cycles_ema, avg, clock, priv->dfs_lowcorner);
+
+            err = nvtegra_channel_set_freq(channel, clock);
+
+            priv->dfs_last_ts_delta = wl_dt;
+        }
+
+        priv->dfs_bitrate_sum       = 0;
+        priv->dfs_sampling_start_ts = now;
+    }
+
+    return err;
+}
+
+int av_nvtegra_dfs_uninit(AVHWDeviceContext *ctx, AVNVTegraChannel *channel) {
+    return nvtegra_channel_set_freq(channel, 0);
+}
+
 static int nvtegra_transfer_get_formats(AVHWFramesContext *ctx,
                                         enum AVHWFrameTransferDirection dir,
                                         enum AVPixelFormat **formats)
diff --git a/libavutil/hwcontext_nvtegra.h b/libavutil/hwcontext_nvtegra.h
index 8a2383d304..7c845951d9 100644
--- a/libavutil/hwcontext_nvtegra.h
+++ b/libavutil/hwcontext_nvtegra.h
@@ -82,4 +82,11 @@ static inline AVNVTegraMap *av_nvtegra_frame_get_fbuf_map(const AVFrame *frame)
  */
 int av_nvtegra_pixfmt_to_vic(enum AVPixelFormat fmt);
 
+/*
+ * Dynamic frequency scaling routines
+ */
+int av_nvtegra_dfs_init(AVHWDeviceContext *ctx, AVNVTegraChannel *channel, int width, int height, double framerate_hz);
+int av_nvtegra_dfs_update(AVHWDeviceContext *ctx, AVNVTegraChannel *channel, int bitstream_len, int decode_cycles);
+int av_nvtegra_dfs_uninit(AVHWDeviceContext *ctx, AVNVTegraChannel *channel);
+
 #endif /* AVUTIL_HWCONTEXT_NVTEGRA_H */
-- 
2.45.1

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