FPS Detection

Auriya reports a frames-per-second value in daemon status and, when Frame-Aware Scheduling is active, feeds frame data to the scheduler. FPS observation and FAS control are separate: this page covers observation (src/core/fps_meter/mod.rs); FAS is documented in Kala eBPF frame probe and Profile scheduler.

Traced to Auriya commit 10fe7c6, src/core/fps_meter/mod.rs.

Two sources, sysfs first

FpsMeter::read tries sysfs, and only falls back to eBPF frame deltas if sysfs yields nothing (fps_meter/mod.rs, read()). Sysfs is preferred because it reports the actual display-measured refresh, which is steadier than per-frame deltas under triple-buffering or vsync lock (module doc comment).

Every reading carries its origin so consumers can tell them apart:

pub enum FpsSource { Ebpf, Sysfs }
pub struct FpsReading { pub fps: f64, pub source: FpsSource }

flowchart TD
    req([FPS Request]) --> check_sysfs{"Sysfs Node Available?"}
    check_sysfs -->|yes| sysfs_cache{"Cache < 2s old?"}
    sysfs_cache -->|yes| return_cached["Return cached sysfs reading"]
    sysfs_cache -->|no| read_node["Read /sys node (f64)"]
    read_node --> check_val{"0 < value ≤ 500?"}
    check_val -->|yes| return_sysfs["Return FpsReading (Sysfs)"]
    check_val -->|no / empty| fallback_ebpf

    check_sysfs -->|no| fallback_ebpf{"eBPF Frame Stream Available?"}
    fallback_ebpf -->|no| return_none["Return None"]
    fallback_ebpf -->|yes| drain["Drain deltas < 500ms into 30-frame ring"]
    drain --> check_ring{"Frames in last 3s?"}
    check_ring -->|no| return_none
    check_ring -->|yes| calc["Calculate 1.0 / mean(frametimes)"]
    calc --> clamp{"0 < FPS ≤ 500?"}
    clamp -->|yes| return_ebpf["Return FpsReading (Ebpf)"]
    clamp -->|no| return_none

In STATUS this surfaces as FPS=<value> SOURCE=<ebpf|sysfs> (see IPC protocol → STATUS).

Sysfs source

At construction, detect_sysfs() probes this ordered list and picks the first path that exists and is non-empty (FPS_SYSFS_PATHS, fps_meter/mod.rs):

/sys/class/drm/sde-crtc-0/measured_fps
/sys/class/drm/card0/sde-crtc-0/measured_fps
/sys/class/drm/card0/sde_crtc_fps
/sys/class/drm/card0/fbc/fps
/sys/class/graphics/fb0/measured_fps
/sys/class/graphics/fb0/fps
/sys/kernel/debug/mali/fps
/sys/class/misc/mali0/device/fps

The first six are Qualcomm/DRM display-controller and framebuffer nodes; the last two are Mali (ARM GPU) nodes. If none qualify, there is no sysfs source and the meter relies on eBPF only.

Behavior (read_sysfs):

• Polled at most once every 2 seconds (SYSFS_POLL_INTERVAL); between polls the last reading is returned from cache.
• The file is parsed as f64; values outside (0, 500] are rejected (returns None), guarding against garbage or a 0 reading when the panel is idle.

eBPF fallback

Used only when sysfs produced nothing. Frame durations arrive over a broadcast::Receiver<Duration> from the Kala frame stream (see Kala eBPF frame probe → Auriya integration). drain_ebpf + read (fps_meter/mod.rs):

• Each incoming delta is kept only if < 500 ms (Duration::from_millis(500)); larger gaps (app not rendering) are dropped.
• Kept deltas fill a 30-frame ring (SHORT_WINDOW, ≈ ½ s at 60 fps); FPS is 1.0 / mean(frametimes).
• If no frame has arrived for 3 seconds (ebpf_timeout), or the ring is empty, read returns None.
• The computed FPS is subject to the same (0, 500] sanity clamp.
• A lagged broadcast (TryRecvError::Lagged) is logged and skipped; a closed channel disables the eBPF source for the rest of the meter’s life.

Consequences

• FAS availability does not gate status FPS. Even when the eBPF program cannot attach (old kernel, missing symbols), sysfs FPS still populates status.
• The meter never blocks: sysfs is cache-throttled, eBPF is drained non-blocking. A tick that finds neither source simply reports no FPS.
• The eBPF value here is a frame-submission rate derived from queueBuffer deltas, not a display-present timestamp — see the limitations in Kala eBPF frame probe → Scope and limitations.

Likely to drift first

FPS_SYSFS_PATHS (device-specific), the 2 s / 3 s / 500 ms / 30-frame constants, and the (0, 500] clamp. Re-verify against src/core/fps_meter/mod.rs.