From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C30F9C48BCD for ; Thu, 10 Jun 2021 08:27:27 +0000 (UTC) Received: from alsa0.perex.cz (alsa0.perex.cz [77.48.224.243]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 16C32613E7 for ; Thu, 10 Jun 2021 08:27:26 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 16C32613E7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=sakamocchi.jp Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=alsa-devel-bounces@alsa-project.org Received: from alsa1.perex.cz (alsa1.perex.cz [207.180.221.201]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by alsa0.perex.cz (Postfix) with ESMTPS id 3D7E1174C; Thu, 10 Jun 2021 10:26:34 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa0.perex.cz 3D7E1174C DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=alsa-project.org; s=default; t=1623313644; bh=T5u46DeceMIm98MPI0jpwLUpur/aGxEyrG1kt3ixu4s=; h=Date:From:To:Subject:References:In-Reply-To:Cc:List-Id: List-Unsubscribe:List-Archive:List-Post:List-Help:List-Subscribe: From; b=RrCXR2UGNLZM3spzlNjI79z2tTt4NkYFTqo1Fl1z/yx20qTrNo2Znr49FTfszMlVj Nxoraw0y+CaTa06jvWB+dgxiPG8YMOm5HU/3ErM91xEq5tvLHOTSh/FoEN0CzLCvqr HxJKchB3/czn8vr02w5RS7BTY0ZmMKmGo3pIiDBU= Received: from alsa1.perex.cz (localhost.localdomain [127.0.0.1]) by alsa1.perex.cz (Postfix) with ESMTP id CB6B6F8020D; Thu, 10 Jun 2021 10:26:33 +0200 (CEST) Received: by alsa1.perex.cz (Postfix, from userid 50401) id 5C21AF80218; Thu, 10 Jun 2021 10:26:32 +0200 (CEST) Received: from out4-smtp.messagingengine.com (out4-smtp.messagingengine.com [66.111.4.28]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by alsa1.perex.cz (Postfix) with ESMTPS id 9785EF80149 for ; Thu, 10 Jun 2021 10:26:27 +0200 (CEST) DKIM-Filter: OpenDKIM Filter v2.11.0 alsa1.perex.cz 9785EF80149 Authentication-Results: alsa1.perex.cz; dkim=pass (2048-bit key) header.d=sakamocchi.jp header.i=@sakamocchi.jp header.b="C4M10c/W"; dkim=pass (2048-bit key) header.d=messagingengine.com header.i=@messagingengine.com header.b="Yqfi5sk7" Received: from compute3.internal (compute3.nyi.internal [10.202.2.43]) by mailout.nyi.internal (Postfix) with ESMTP id 68C185C0159; Thu, 10 Jun 2021 04:26:26 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute3.internal (MEProxy); Thu, 10 Jun 2021 04:26:26 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=sakamocchi.jp; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:in-reply-to; s=fm1; bh=SvS9jsdkFqw5BICUSSLlRxm9v3y ogA5bCSduNQcqQ08=; b=C4M10c/WMA0C6p59bWRlprWdjG7JjvfaQRb43wjCT98 FGvN/CKGQpORemN5BMAEaJuePdFgtdHavJZDcKbYGNDUqa5ewaWiqO3lK5SBM+Ah omUa+ME64R9f5bA/wbMd5YvqwWZTErd8QjbSUg/+VkA+cGxLjRLN51E5SmzcjxdF q2fogWcTr0rvxSNFTv4IfW2Sois2/CpWvwxwGyD1ULEkHP3wHw8yMitLAVgGYBx5 C+ppOuwpkbk3ktp+DjMS6Gbq4wQoICtcAF/67Pad17f3f06p1F4GjNUoRUkxJy9n DXgHdvitrnv0oCPIq+x2Kchmp33AYeFYHsKQiEMX2PA== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to:x-me-proxy :x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s=fm3; bh=SvS9js dkFqw5BICUSSLlRxm9v3yogA5bCSduNQcqQ08=; b=Yqfi5sk7OZELqEfVlqbxkK 5f8aL0V+dffXr6EKIolnRCJL/aB/TdcTmXmWgjxpAlGZAjw8H+yHvJbaPWAxOYEi W3WDFtaWkEYMKV4mxU/YglXtUZGfH6BAALbnPq+p3zUDToi86b93EU1w+81QYmwl e2GxPdHv5U+BbB+OvUQq4bZl+iQU4ydgy2aI4n1R4QUWu165ndfsfDO7oQ0JULiL a74ZUJAaNQ21tGeZ891PALHe+vLG+IVz+S68H4bz8hqYNPnY3su1gpNDVXry6V3Q 50/IJoMrPZ+PhoOhxxuJvz3fqtyUBd/+R3tYpysaVg26VJ6q9VAokoozi7QUKuaQ == X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgeduledrfedufedgtddvucetufdoteggodetrfdotf fvucfrrhhofhhilhgvmecuhfgrshhtofgrihhlpdfqfgfvpdfurfetoffkrfgpnffqhgen uceurghilhhouhhtmecufedttdenucesvcftvggtihhpihgvnhhtshculddquddttddmne cujfgurhepfffhvffukfhfgggtuggjsehttdertddttddvnecuhfhrohhmpefvrghkrghs hhhiucfurghkrghmohhtohcuoehoqdhtrghkrghshhhisehsrghkrghmohgttghhihdrjh hpqeenucggtffrrghtthgvrhhnpeelhfeugedvjefgjefgudekfedutedvtddutdeuieev tddtgeetjeekvdefgeefhfenucevlhhushhtvghrufhiiigvpedtnecurfgrrhgrmhepmh grihhlfhhrohhmpehoqdhtrghkrghshhhisehsrghkrghmohgttghhihdrjhhp X-ME-Proxy: Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 10 Jun 2021 04:26:24 -0400 (EDT) Date: Thu, 10 Jun 2021 17:26:22 +0900 From: Takashi Sakamoto To: Takashi Iwai Subject: Re: [PATCH v2 1/3] ALSA: pcm: add snd_pcm_period_elapsed() variant without acquiring lock of PCM substream Message-ID: <20210610082622.GA86308@workstation> Mail-Followup-To: Takashi Iwai , clemens@ladisch.de, alsa-devel@alsa-project.org References: <20210609143145.146680-1-o-takashi@sakamocchi.jp> <20210609143145.146680-2-o-takashi@sakamocchi.jp> <20210609231623.GA3207@workstation> <20210610080521.GA84899@workstation> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Cc: alsa-devel@alsa-project.org, clemens@ladisch.de X-BeenThere: alsa-devel@alsa-project.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: "Alsa-devel mailing list for ALSA developers - http://www.alsa-project.org" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: "Alsa-devel" On Thu, Jun 10, 2021 at 10:08:39AM +0200, Takashi Iwai wrote: > On Thu, 10 Jun 2021 10:05:21 +0200, > Takashi Sakamoto wrote: > > > > On Thu, Jun 10, 2021 at 09:39:37AM +0200, Takashi Iwai wrote: > > > On Thu, 10 Jun 2021 01:16:23 +0200, > > > Takashi Sakamoto wrote: > > > > > > > > On Wed, Jun 09, 2021 at 05:27:29PM +0200, Takashi Iwai wrote: > > > > > On Wed, 09 Jun 2021 16:31:43 +0200, > > > > > Takashi Sakamoto wrote: > > > > > > diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c > > > > > > index b7e3d8f44511..3488ec1e3674 100644 > > > > > > --- a/sound/core/pcm_lib.c > > > > > > +++ b/sound/core/pcm_lib.c > > > > > > @@ -1778,27 +1778,41 @@ int snd_pcm_lib_ioctl(struct snd_pcm_substream *substream, > > > > > > EXPORT_SYMBOL(snd_pcm_lib_ioctl); > > > > > > > > > > > > /** > > > > > > - * snd_pcm_period_elapsed - update the pcm status for the next period > > > > > > - * @substream: the pcm substream instance > > > > > > + * snd_pcm_period_elapsed_under_stream_lock() - update the status of runtime for the next period > > > > > > + * under acquired lock of PCM substream. > > > > > > + * @substream: the instance of pcm substream. > > > > > > + * > > > > > > + * This function is called when the batch of audio data frames as the same size as the period of > > > > > > + * buffer is already processed in audio data transmission. > > > > > > + * > > > > > > + * The call of function updates the status of runtime with the latest position of audio data > > > > > > + * transmission, checks overrun and underrun over buffer, awaken user processes from waiting for > > > > > > + * available audio data frames, sampling audio timestamp, and performs stop or drain the PCM > > > > > > + * substream according to configured threshold. > > > > > > + * > > > > > > + * The function is intended to use for the case that PCM driver operates audio data frames under > > > > > > + * acquired lock of PCM substream; e.g. in callback of any operation of &snd_pcm_ops in process > > > > > > + * context. In any interrupt context, it's preferrable to use ``snd_pcm_period_elapsed()`` instead > > > > > > + * since lock of PCM substream should be acquired in advance. > > > > > > * > > > > > > - * This function is called from the interrupt handler when the > > > > > > - * PCM has processed the period size. It will update the current > > > > > > - * pointer, wake up sleepers, etc. > > > > > > + * Developer should pay enough attention that some callbacks in &snd_pcm_ops are done by the call of > > > > > > + * function: > > > > > > * > > > > > > - * Even if more than one periods have elapsed since the last call, you > > > > > > - * have to call this only once. > > > > > > + * - .pointer - to retrieve current position of audio data transmission by frame count or XRUN state. > > > > > > + * - .trigger - with SNDRV_PCM_TRIGGER_STOP at XRUN or DRAINING state. > > > > > > + * - .get_time_info - to retrieve audio time stamp if needed. > > > > > > + * > > > > > > + * Even if more than one periods have elapsed since the last call, you have to call this only once. > > > > > > + * > > > > > > + * Context: Any context in which lock of PCM substream is already acquired. This function may not > > > > > > + * sleep. > > > > > > > > > > Hm, this text still remains here. Overlooked? > > > > > > > > It's my intension for documentation of > > > > snd_pcm_period_elapsed_under_stream_lock() since it's expected to call > > > > it under acquired lock. Its implementation doesn't yield processor > > > > voluntarily by itself. If it yielded, it would depend on implementation > > > > of each driver for struct snd_pcm_ops.{pointer, trigger, get_time_info}, > > > > but it's not preferable implementation of driver, in my opinion. > > > > > > My point is again about the sleep. This function may sleep in the > > > nonatomic mode. The type of the PCM stream lock depends on it. > > > > Would I simply request you to show how the added function yields except > > for the driver implementation? The lock of stream is expected to be > > acquired already. > > In the nonatomic mode, the PCM stream lock is a mutex (no > spin_lock_irqsave), hence it can sleep -- which contradicts with the > added description above. > > Or do I misunderstand your question...? Thanks to clarify the role of PCM stream lock, and I'm ease that we have the same understanding about the lock. Here, let us see deleted/added line again. > diff --git a/sound/core/pcm_lib.c b/sound/core/pcm_lib.c > index b7e3d8f44511..3488ec1e3674 100644 > --- a/sound/core/pcm_lib.c > +++ b/sound/core/pcm_lib.c > @@ -1778,27 +1778,41 @@ int snd_pcm_lib_ioctl(struct snd_pcm_substream *substream, > EXPORT_SYMBOL(snd_pcm_lib_ioctl); > > /** > - * snd_pcm_period_elapsed - update the pcm status for the next period > - * @substream: the pcm substream instance > + * snd_pcm_period_elapsed_under_stream_lock() - update the status of runtime for the next period > + * under acquired lock of PCM substream. > + ... > + * Context: Any context in which lock of PCM substream is already acquired. This function may not > + * sleep. The issued documentation is for the new function. Inner the function, the lock of PCM substream is not acquired again since it causes dead lock (it's not nest-able lock) regardless of usage of mutex or spin_lock. The well-known function, snd_pcm_period_elapsed(), is rewritten to call the new function between lock/unlock operations: ->snd_pcm_period_elapsed() ->snd_pcm_stream_lock_irqsave() ->snd_pcm_period_elapsed_under_stream_lock() ->snd_pcm_stream_unlock_irqrestore() Or the new function can acquire the lock somewhere I overlook? However I think it is unlikely since it necessarily causes dead lock or corruption of irq context... Thanks Takashi Sakamoto