Re: [RFC] SAL_MC_RENDEZ logic

From: Hidetoshi Seto <seto.hidetoshi_at_jp.fujitsu.com>
Date: 2005-09-12 18:27:44
Thank you for your reply, Keith.

Keith Owens wrote:
> The IRR bits are read only.  The OS clears them by reading cr.ivr, in
> the external interrupt vector.  The only reason that mca.c tests IRR
> directly is because at that point interrupts are disabled.

I forgot to mention, the SAL actually reads cr.ivr and writes cr.eoi.

>>I'm not sure but it seems "if any" means that SAL can clear
>>the IRR bits on behalf of OS.  So OS shouldn't expect the IRR
>>always be set on returning from SAL_MC_RENDEZ, is this right?
> 
> The phrase "if any" is quite ambiguous, it is not clear what it means
> here.

I agree.  It should be written in full sentence.

>>I don't know whether there is any old SAL never spins in
>>SAL_MC_RENDEZ or not.  Or is this the beginning of nightmare,
>>having different MCA codes depend on the SAL version?
> 
> I hope not.  In any case my MCA/INIT rewrite removes the spin in mca.c
> waiting for IRR to be set.  Instead the slave comes out of SAL due to a
> wake up call, waits for the monarch to exit then the slaves all exit.
> 
> Once a slave resumes to its normal context and interrupts are enabled
> again, then the external interrupt vector clears the wake up bit and
> calls ia64_mca_wakeup_int_handler() which is a no-op.  The rendezvous
> IRR bit is cleared when we read cr.ivr prior to calling
> ia64_mca_rendez_int_handler(), i.e. this bit is already clear when we
> rendezvous.
> 
> In your case I would say that SAL is wrong.  I would argue that SAL
> should not be reading cr.ivr at all, it should leave that to the OS.
> The existing (2.6.13) code will not work with that SAL.  My rewrite
> (hopefully in 2.6.14-rc1) will work with that SAL.

I appreciate your work very well.
I'll argue off this problem with developers of the SAL instead of you.

Thanks,
H.Seto

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Received on Mon Sep 12 18:29:01 2005

This archive was generated by hypermail 2.1.8 : 2005-09-12 18:29:10 EST