Re: [microblaze-uclinux] Interrupts disabled in RETURN macro

[Alejandro Lucero <alucero@xxxxxxxxx>]

On Wednesday 19 April 2006 03:51, John Williams wrote:
> Hi Alejando,

> Your patch works for me (that is, it doesn't crash - mayjor bugs in
> entry.S usually show themselves pretty quickly).

I'm not sure about it. I have discovered a problem, well, really I have just 
discovered the effect ;-)
I think my proposal is right at least in theory. Perhaps we can do that but 
some special code must be protected and I have not seen it (still).
>
> Do you think the problem you were seeing under high interrupt load was
> because an IRQ was squeezing inside the state restore?  Previously (pre
> your patch) interrupts should have been disabled during that phase, but
> fdorcing BIP makes extra sure I suppose.

I dont understand what you want to say. I have taken measures and with my 
proposal the latencies are not better, but it's simply because I don't have 
enough processes or syncs with signals in my tests, which is where the 
problem would be.
 
> >>>Delaying disabling interrupts would improve interrupts latency since
> >>> less code would be executed with interrupts disabled.
> Yes, that seems reasonable.

That's my point although the measurement doesn't show this.

> >>>I have tested this approach and it works even with high interrupts
> >>>frequency. Perhaps I'm forgetting something and in this way some race
> >>>condition can happen and it's hard to reproduce in my tests.
>
> I've attached a modified version of your patch, which implements the
> same changes (plus applies same logic to the debug trap), and goes a bit
> further to cleanup comments and makes better use of the delay slot on
> branch and return instructions wwere possible - since we're in the mood
> for saving cycles... :)
> Can you, (and as many others as possible please) try this, and see it it
> works for you?  Applies against current CVS head.

I'll do it, but now I want to study the problem found. I'll keep you inform 
about my discoveries.

> Thanks,
>
> John

-- 
Alejandro Lucero
Technical Director
+34 665 68 71 68
Valencia (SPAIN)
www.os3sl.com
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