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Message-ID: <14DF3A68-94EE-499E-9B67-635CAF0AD6C7@intel.com>
Date: Tue, 20 May 2014 17:06:17 +0000
From: "Rustad, Mark D" <mark.d.rustad@...el.com>
To: Andi Kleen <ak@...ux.intel.com>
CC: Andi Kleen <andi@...stfloor.org>,
"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>,
"<linux-kernel@...r.kernel.org>" <linux-kernel@...r.kernel.org>,
"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH 1/8] ixgbe: Out of line ixgbe_read/write_reg
On May 19, 2014, at 4:25 PM, Andi Kleen <ak@...ux.intel.com> wrote:
> 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@...stfloor.org> wrote:
>>
>>> From: Andi Kleen <ak@...ux.intel.com>
>>>
>>> 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.
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
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