linux-kernel - Re: [PATCH 02/39] x86, PCI: have own version for pcibios_bus_to

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Message-ID: <CAErSpo5N72zkfvvgSNg0MsKAZwcR5TOsxH+Y7BkVbOBYWbdaKQ@mail.gmail.com>
Date:	Wed, 29 Feb 2012 17:42:36 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Tony Luck <tony.luck@...el.com>,
	David Miller <davem@...emloft.net>, x86 <x86@...nel.org>,
	Dominik Brodowski <linux@...inikbrodowski.net>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 02/39] x86, PCI: have own version for pcibios_bus_to_resource

On Wed, Feb 29, 2012 at 4:33 PM, Yinghai Lu <yinghai@...nel.org> wrote:
> On Wed, Feb 29, 2012 at 3:20 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
>> On Wed, Feb 29, 2012 at 4:07 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>>> x86 does not need to offset the address. So we can skip that costing offset
>>> searching.
>>
>> I tried to start a discussion about this patch (and others), but I
>> don't think you responded:
>> http://marc.info/?l=linux-pci&m=133036414506921&w=2
>
> this patch does reduce some not needed ops.
>
> and it does not affects your effects,

It does affect my efforts in that this patch adds back x86 complexity
that I don't think is necessary.

And this patch makes it so the pci_add_resource_offset() interface
exists and appears to work on x86, but if somebody tries to use it, it
*doesn't* work.  I don't like to write code like that.  I think it's
poor style.

> and it just make x86 not get punished.

What punishment are you worried about?  I really don't think you'll be
able to measure any performance impact.

I agree that the x86 code you add *is* simpler than the generic
version.  But I think the *overall* complexity is higher because now
you have to look at two versions (generic and x86) and convince
yourself that it's safe to use the x86 version.

Bjorn
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