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From: Kumar Gala <galak@kernel.crashing.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
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Subject: Re: [PATCH] powerpc: Add support for using doorbells for SMP IPI
Date: Thu, 12 Feb 2009 23:10:08 -0600
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On Feb 12, 2009, at 8:46 PM, Benjamin Herrenschmidt wrote:

> On Thu, 2009-02-12 at 17:54 -0600, Kumar Gala wrote:
>> The e500mc supports the new msgsnd/doorbell mechanisms that were  
>> added in
>> the Power ISA 2.05 architecture.  We use the normal level doorbell  
>> for
>> doing SMP IPIs at this point.
>>
>
> Cool stuff. Haven't reviewed in details yet tho :-) But I was
> thinking...
>
> We should introduce a special xmon variant of local_irq_save/restore  
> for
> use by xmon that masks MSR:CE and use a crit doorbell for xmon IPI,  
> that
> would increase significantly the ability of xmon to catch deadlocked
> CPUs, and we could use external CRITs as a more generic way of doing
> IPIs, no ?

crit doorbell for xmon IPI sounds interesting.  However, I don't  
following about use of external CRITs for IPIs.

> In fact, we should expose a local_crit_irq_save/restore (disable/ 
> enable)
> too for things like watchdog drivers etc... which may want to use  
> these.

Yeah, probably a good thing for us to add.

- k