linux-kernel - Re: [PATCH v6 6/9] ALSA: virtio: PCM substream operators

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Message-ID: <f8a4bbf5-3bee-f336-0efd-94410184fb2b@opensynergy.com>
Date:   Mon, 1 Mar 2021 10:29:24 +0100
From:   Anton Yakovlev <anton.yakovlev@...nsynergy.com>
To:     Takashi Iwai <tiwai@...e.de>
CC:     <virtualization@...ts.linux-foundation.org>,
        <alsa-devel@...a-project.org>, <virtio-dev@...ts.oasis-open.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 6/9] ALSA: virtio: PCM substream operators

On 28.02.2021 12:32, Takashi Iwai wrote:
> On Sat, 27 Feb 2021 09:59:53 +0100,
> Anton Yakovlev wrote:
>>


[snip]


>> +static snd_pcm_uframes_t
>> +virtsnd_pcm_pointer(struct snd_pcm_substream *substream)
>> +{
>> +     struct virtio_pcm_substream *vss = snd_pcm_substream_chip(substream);
>> +     snd_pcm_uframes_t hw_ptr = SNDRV_PCM_POS_XRUN;
>> +     unsigned long flags;
>> +
>> +     spin_lock_irqsave(&vss->lock, flags);
>> +     if (!vss->xfer_xrun)
>> +             hw_ptr = bytes_to_frames(substream->runtime, vss->hw_ptr);
>> +     spin_unlock_irqrestore(&vss->lock, flags);
> 
> Oh, and if we drop nonatomc PCM, both trigger and pointer callbacks
> are guaranteed to be called inside the spinlock, hence you can remove
> *_irqsave() but just us spin_lock() in those two callbacks.

As I understand, spin_lock_irqsave() disables only local interrupts. But
what about other CPU cores?


> 
> thanks,
> 
> Takashi
> 

-- 
Anton Yakovlev
Senior Software Engineer

OpenSynergy GmbH
Rotherstr. 20, 10245 Berlin