Re: [PATCH 1/8] ixgbe: Out of line ixgbe_read/write_reg

[Andi Kleen]

On Mon, May 19, 2014 at 10:00:52PM +0000, Rustad, Mark D wrote:
> On May 16, 2014, at 2:43 PM, Andi Kleen <andi@xxxxxxxxxxxxxx> wrote:
> 
> > From: Andi Kleen <ak@xxxxxxxxxxxxxxx>
> > 
> > ixgbe_read_reg and ixgbe_write_reg are frequently called and are very big
> > because they have complex error handling code.
> 
> Actually, this patch doesn't do anything to ixgbe_write_reg, which would almost certainly be very bad for performance, but instead changes ixgbe_write_reg64.

I doubt a few cycles around the write make a lot of difference for MMIO. MMIO is dominated
by other things.

> The latter is not in a performance-sensitive path, but is only called from one site, so there is little reason to take it out-of-line.

True I moved the wrong one.

ixgbe_write_reg                                    3305  (0.00%)  8     409  


> I already have a patch in queue to make ixgbe_read_reg out-of-line, because it does have a very costly memory footprint inline, as you have found.

Please move write_reg too.

-Andi
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