Subject: Re: [PATCH] qe_ic: Do a sync when masking interrupts.

From: Scott Wood <[email-masked]>
Date: Mon, 23 Oct 2006 13:22:57 -0500

Kumar Gala wrote:
> 
> On Oct 23, 2006, at 10:19 AM, Scott Wood wrote:
>> Possibly -- but the only problem on the rare occasions where the  timing
>> is not fortuitous is a spurious interrupt; the only reason the sync
>> needs to be there at all is to avoid the overhead of the extra  interrupt
>> (and to avoid user complaints that they're getting "BAD" interrupts).
> 
> 
> Why wouldn't the read accomplish the same thing in a more robust way  
> than the sync?

It would.  However, it also adds a small amount of overhead to every QE 
interrupt, and the only thing that that overhead buys is avoiding 
possible but empirically very rare spurious interrupts; it'd cost more 
than simply accepting that a spurious interrupt might happen once in a 
great while.

Without any type of sync, spurious interrupts happen fairly regularly 
(about 5-10% of legitimate interrupts), so adding the sync should be a 
net gain over doing nothing.

If the consensus is that a read should be done anyway, I can resumbit 
the patch that way; I just think it's overkill given that a 100% 
guarantee isn't required for correctness.

-Scott