At Sun, 1 Apr 2001 15:48:48 +0100,
Chris Gilbert wrote:
> I've been looking over the irq handling code with a view to speeding it up 
> (although measuring performance isn't very easy)  Anyway I've tweaked the 
> code, got rid of the excessive looping when looking at the irq request field 
> and which bit's are set (it checked every bit) and replaced it with ffs like 
> code.  I've also shifted the ldr's around to try and get rid of load delays 
> causing pipeline stalls.
> 
> I've attached the patch.  If people could take a look and check I've not done 
> anything really daft (it runs, I'm currently doing a make build with it in 
> place :) (or if there's anything else I can do :)  If it looks ok I'll commit 
> it.
> 
> Does anyone know a good way to test the irq handling speed?

Does it make sense to run a userland benchmark program to measure
irq_entry speed?
Although this kind of test cannot predict performance penalty from
cache misses of irq_ffs_table, I suppose it would be somewhat useful.

(I hope this patch is also useful on hpcarm, but cache miss penalty is
quite high there, at least for my jornada720.  lmbench says it takes
300ns to load a cache line...)

--
IWAMOTO Toshihiro