kernel 3.0.8 audio dataflow

最新推荐文章于 2022-11-06 10:35:47 发布

JianqunXu

最新推荐文章于 2022-11-06 10:35:47 发布

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分类专栏： linux kernel 文章标签： audio playback stream signal linux 工作

本文链接：https://blog.youkuaiyun.com/xujianqun/article/details/6954484

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本文对比分析了Linux内核2.6.32与3.0.8中音频子系统的代码实现差异，特别是在等待可用空间及信号处理方面进行了深入探讨，指出了代码优化之处。

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kernel 2.6.32

	for (;;) {
		if (signal_pending(current)) {
			err = -ERESTARTSYS;
			break;
		}
		set_current_state(TASK_INTERRUPTIBLE);
		snd_pcm_stream_unlock_irq(substream);
		tout = schedule_timeout(msecs_to_jiffies(10000));
		snd_pcm_stream_lock_irq(substream);

kernel 3.0.8

	if (runtime->no_period_wakeup)
		wait_time = MAX_SCHEDULE_TIMEOUT;
	else {
		wait_time = 10;
		if (runtime->rate) {
			long t = runtime->period_size * 2 / runtime->rate;
			wait_time = max(t, wait_time);
		}
		wait_time = msecs_to_jiffies(wait_time * 1000);
	}

	for (;;) {
		if (signal_pending(current)) {
			err = -ERESTARTSYS;
			break;
		}

		/*
		 * We need to check if space became available already
		 * (and thus the wakeup happened already) first to close
		 * the race of space already having become available.
		 * This check must happen after been added to the waitqueue
		 * and having current state be INTERRUPTIBLE.
		 */
		if (is_playback)
			avail = snd_pcm_playback_avail(runtime);
		else
			avail = snd_pcm_capture_avail(runtime);
		if (avail >= runtime->twake)
			break;
		snd_pcm_stream_unlock_irq(substream);

		tout = schedule_timeout(wait_time);

		snd_pcm_stream_lock_irq(substream);

之前看到kernel这地方代码，就觉得linux怎么也会放这种错误，低级的垃圾代码，虽然目前有点工作是在这里动手，但是还是觉得不合理

晚上忍不住时间看了3.0.8代码，直接奔这儿来了，没失望，有收获，有时间继续看~~