linux-kernel - Re: [PATCH] PCI: conditional resource-reallocation through kernel parameter pci=realloc

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Date:	Thu, 30 Jun 2011 13:26:16 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Ram Pai <linuxram@...ibm.com>,
	Oliver Hartkopp <socketcan@...tkopp.net>,
	torvalds@...ux-foundation.org, linux-pci@...r.kernel.org,
	linux-kernel@...r.kernel.org, yinghai@...nel.org
Subject: Re: [PATCH] PCI: conditional resource-reallocation through kernel
 parameter pci=realloc

On Thu, 30 Jun 2011 14:24:24 -0600
Bjorn Helgaas <bhelgaas@...gle.com> wrote:

> On Thu, Jun 30, 2011 at 12:38 PM, Ram Pai <linuxram@...ibm.com> wrote:
> > On Thu, Jun 30, 2011 at 07:12:38PM +0200, Oliver Hartkopp wrote:
> >> On 30.06.2011 19:07, Jesse Barnes wrote:
> >> > On Thu, 30 Jun 2011 19:04:55 +0200
> >> > Oliver Hartkopp <socketcan@...tkopp.net> wrote:
> >> >
> >> >> On 30.06.2011 10:09, Ram Pai wrote:
> >> >>> Multiple attempts to dynamically reallocate pci resources have unfortunately
> >> >>> lead to regressions. Though we continue to fix the regressions and fine tune the
> >> >>> dynamic-reallocation behavior, we have not reached a acceptable state yet.
> >> >>>
> >> >>> This patch provides a interim solution. It disables dynamic-reallocation; by
> >> >>> default, with the ability to enable it through pci=realloc kernel command line
> >> >>> parameter.
> >> >>
> >> >> What is the advantage of creating an 'interim' kernel parameter instead of
> >> >> reverting the problematic commit and queue up a proper solution for 3.1 ?
> >> >>
> >> >> A kernel parameter needs to be observed, documented and set appropriately.
> >> >>
> >> >> I would prefer to have an automatic solution - if not in 3.0 then in 3.1 ...
> >> >
> >> > Yeah, we all want an automatic solution, but we still haven't been able
> >> > to achieve one.  My hope is that a parameter will let us keep the code
> >> > upstream for Ram and others to keep fixing, then we can move to using
> >> > it by default in some future release.  Keeping the code upstream but
> >> > behind a param should make development easier; at least that's the goal.
> >>
> >> What's wrong with the "[PATCH 0/4 v2] PCI: fix cardbus and sriov regressions"?
> >> To me it looked good - or don't you trust that fix right now?
> >
> > I trust the fix :).
> >
> > Linus's concern was the wrong alignment, which I have fixed, but yet to resend
> > the patchset. Will do today.
> >
> > However Linus's other concern was "too late for 3.0.0, for such a large patch".
> >
> > There is the other concern about "should cardbus resources be treated nice-to-have?"
> 
> Somewhere along the way, can we get rid of the awkward "nice-to-have"
> language?  I think "optional" conveys most of the intended meaning,
> perhaps lacking the shade that "we'll allocate them if we can."  But
> the important part is that they are not *required*, and "optional" is
> a nice antonym for "required."

I think there's a lot more that could be cleaned up in the re-alloc
code; e.g. add_head isn't very descriptive as a way to pass around
resources that we're tracking for potential re-allocation.

-- 
Jesse Barnes, Intel Open Source Technology Center
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