Re: [PATCH] cs46xx: once again SMP fixes, new aproach

[Takashi Iwai <tiwai@suse.de>]

At Thu, 22 Aug 2002 23:29:20 +0200,
Benny Sjostrand wrote:
> 
> 
> - The pcm_link/unlink only access SCB under it's related SRCTask_SCB*, 
> it only touches the nex_scb_ptr, parent_ptr and sub_list_ptr on 
> SRCTask.. so it can safely be running paralel with any other 
> simultaneous operation on other parts of the tree, and it can be running 
> paralell with others pcm_link/unlink related to other SRCTask*.
> 
> - In create_pcm_channel the channel is initially created unlinked, which 
> mean pcm_link must be called before playback start, invoked by 
> playback_trigger. Anyway pcm_unlink was called in playback_open, which 
> now can be removed. In this way the pcm_reader SCB will be initially 
> floating, with no parent SCB and therefor we dont need any spin_lock in 
> create_pcm_channel.
> 
> - But, the _same_ PCM stream, playback_trigger cant run before  
> playback_open has completed. Which make no sense,  I supose the ALSA PCM 
> core prevent a process from doing this to happen.
 
this must be ok.

> - In pcm_link the PCMReaderSCB is always linked in after SRCTask* 
> sub_list_ptr, then therefor is no need loop searching for the last free 
> SCB in sublist.
 
good, that's somewhat i thought of.

> Conclusion what we got is:
> - No mutexes in playback_trigger
> - Independent spin_locks for each SRCTask*
> - spin_lock only needed in pcm_link/unlink and in cs46xx_dsp_remove_scb.
 
great!
the patch looks more cleaner than before.

> With fewer and short spin_locks, theorically we manage to have good 
> performance on SMP machines -:)
> 
> That's all, ... i think ...
> Question, suggestion or whatever you got in mind about this is welcome, 
> i'll try to be open.

i'll try to run and merge to cvs later.


thanks!


Takashi


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