linux-kernel - Re: [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi

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Message-ID: <20130926130328.GD16774@dhcp-26-207.brq.redhat.com>
Date:	Thu, 26 Sep 2013 15:03:29 +0200
From:	Alexander Gordeev <agordeev@...hat.com>
To:	Mark Lord <kernel@...rt.ca>
Cc:	Michael Ellerman <michael@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Tejun Heo <tj@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-ide@...r.kernel.org" <linux-ide@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>, Joerg Roedel <joro@...tes.org>,
	Jan Beulich <JBeulich@...e.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi_cap() interface

On Thu, Sep 26, 2013 at 08:32:53AM -0400, Mark Lord wrote:
> On 13-09-18 05:48 AM, Alexander Gordeev wrote:
> > The last pattern makes most of sense to me and could be updated with a more
> > clear sequence - a call to (bit modified) pci_msix_table_size() followed
> > by a call to pci_enable_msix(). I think this pattern can effectively
> > supersede the currently recommended "loop" practice.
> 
> The loop is still necessary, because there's a race between those two calls,
> so that pci_enable_msix() can still fail due to lack of MSIX slots.

Moreover, the existing loop pattern is racy and could fail just as easily ;)
But (1) that is something drivers should expect and (2) there is basically
nothing to race against - that is probably the reason it has not been a
problem for pSeries. So I think we should not care about this.

-- 
Regards,
Alexander Gordeev
agordeev@...hat.com
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