On Thu, Dec 17, 2015 at 02:35:34PM +0200, Saeed Mahameed wrote:
> @@ -63,6 +65,7 @@
> #define MLX5E_TX_CQ_POLL_BUDGET 128
> #define MLX5E_UPDATE_STATS_INTERVAL 200 /* msecs */
> #define MLX5E_SQ_BF_BUDGET 16
> +#define MLX5E_SERVICE_TASK_DELAY (HZ / 4)
Hm...
> +void mlx5e_timestamp_overflow_check(struct mlx5e_priv *priv)
> +{
> + bool timeout = time_is_before_jiffies(priv->tstamp.last_overflow_check +
> + priv->tstamp.overflow_period);
> + unsigned long flags;
> +
> + if (timeout) {
> + write_lock_irqsave(&priv->tstamp.lock, flags);
> + timecounter_read(&priv->tstamp.clock);
> + write_unlock_irqrestore(&priv->tstamp.lock, flags);
> + priv->tstamp.last_overflow_check = jiffies;
Here you have extra book keeping, because the rate of the work
callbacks is not the same as the rate of the overflow checks.
> + }
> +}
> +void mlx5e_timestamp_init(struct mlx5e_priv *priv)
> +{
> + struct mlx5e_tstamp *tstamp = &priv->tstamp;
> + u64 ns;
> + u64 frac = 0;
> + u32 dev_freq;
> +
> + mlx5e_timestamp_init_config(tstamp);
> + dev_freq = MLX5_CAP_GEN(priv->mdev, device_frequency_khz);
> + if (!dev_freq) {
> + mlx5_core_warn(priv->mdev, "invalid device_frequency_khz. %s
> failed\n",
> + __func__);
> + return;
> + }
> + rwlock_init(&tstamp->lock);
> + memset(&tstamp->cycles, 0, sizeof(tstamp->cycles));
> + tstamp->cycles.read = mlx5e_read_clock;
> + tstamp->cycles.shift = MLX5E_CYCLES_SHIFT;
> + tstamp->cycles.mult = clocksource_khz2mult(dev_freq,
> + tstamp->cycles.shift);
> + tstamp->nominal_c_mult = tstamp->cycles.mult;
> + tstamp->cycles.mask = CLOCKSOURCE_MASK(41);
> +
> + timecounter_init(&tstamp->clock, &tstamp->cycles,
> + ktime_to_ns(ktime_get_real()));
> +
> + /* Calculate period in seconds to call the overflow watchdog - to make
> + * sure counter is checked at least once every wrap around.
> + */
> + ns = cyclecounter_cyc2ns(&tstamp->cycles, tstamp->cycles.mask, frac,
> + &frac);
> + do_div(ns, NSEC_PER_SEC / 2 / HZ);
> + tstamp->overflow_period = ns;
> +}
And here you take great pains to calculate the rate of overflow checks...
> +/* mlx5e_service_task - Run service task for tasks that needed to be done
> + * periodically
> + */
> +static void mlx5e_service_task(struct work_struct *work)
> +{
> + struct delayed_work *dwork = to_delayed_work(work);
> + struct mlx5e_priv *priv = container_of(dwork, struct mlx5e_priv,
> + service_task);
> +
> + mutex_lock(&priv->state_lock);
> + if (test_bit(MLX5E_STATE_OPENED, &priv->state) &&
> + !test_bit(MLX5E_STATE_DESTROYING, &priv->state)) {
> + if (MLX5_CAP_GEN(priv->mdev, device_frequency_khz)) {
> + mlx5e_timestamp_overflow_check(priv);
> + /* Only mlx5e_timestamp_overflow_check is called from
> + * this service task. schedule a new task only if clock
> + * is initialized. if changed, move the scheduler.
> + */
> + schedule_delayed_work(dwork, MLX5E_SERVICE_TASK_DELAY);
Why not simply use the rate you calculated, rather than some hard
coded value?
Consider What happens if MLX5E_SERVICE_TASK_DELAY is too long or way
too short.
> + }
> + }
> + mutex_unlock(&priv->state_lock);
> +}
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