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

On May 19, 2014, at 4:25 PM, Andi Kleen [off-list ref] wrote:

On Mon, May 19, 2014 at 10:00:52PM +0000, Rustad, Mark D wrote:

quoted

On May 16, 2014, at 2:43 PM, Andi Kleen [off-list ref] wrote:

quoted

From: Andi Kleen <redacted>

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.

quoted

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  

quoted

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.

I will take a look at moving most of them out-of-line. There are just a few in very hot paths that should remain inline.

-- 
Mark Rustad, Networking Division, Intel Corporation