linux-kernel - Re: [Patch Part2 v4 20/31] PCI/MSI: Kill redundant calling for irq_set_msi

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Date:	Thu, 06 Nov 2014 12:31:02 +0800
From:	Jiang Liu <jiang.liu@...ux.intel.com>
To:	Yijing Wang <wangyijing@...wei.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>
CC:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Randy Dunlap <rdunlap@...radead.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Grant Likely <grant.likely@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tony Luck <tony.luck@...el.com>,
	Joerg Roedel <joro@...tes.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [Patch Part2 v4 20/31] PCI/MSI: Kill redundant calling for irq_set_msi_desc()
 for MSIx interrupts

On 2014/11/6 9:32, Yijing Wang wrote:
> On 2014/11/6 6:45, Bjorn Helgaas wrote:
>> On Tue, Nov 04, 2014 at 08:01:54PM +0800, Jiang Liu wrote:
>>> It's arch_setup_msi_irq()/arch_setup_msi_irqs()'s responsibility to call
>>> irq_set_msi_desc() to associate IRQ descriptors and MSI descriptors,
>>> so kill the redundant call of irq_set_msi_desc() for MSIx interrupts
>>> in PCI MSI core.
>>
>> "MSI-X" in English text, "msix" in code.
>>
>> The default arch_setup_msi_irq() in drivers/pci/msi.c doesn't call
>> irq_set_msi_desc().  Does it happen somewhere inside chip->setup_irq()?
> 
> Yes.
> 
> I also found this.
> http://www.spinics.net/lists/linux-pci/msg34256.html
> 
>>
>> I don't know how to verify that there are calls in all the places needed.
>> That makes me wonder if the factoring is wrong -- maybe irq_set_msi_desc()
>> could be done in some common place.
> 
> In my idea, place the irq_set_msi_desc() in common MSI core is ok, but currently almost
> all MSI arch code call irq_set_msi_desc() in arch code. So a lot of code need to change.
> And arch code setup MSI and MSI-X in the same way, so if MSI work happy without irq_set_msi_desc(entry->irq, entry)
> in common MSI code, MSI-X should be the same.
Hi Bjorn and Yijing,
	I originally plan was to move irq_set_msi_desc() into common
PCI MSI code. But when implementing this, I found every
arch_setup_msi_irq()/arch_setup_msi_irqs() needs to set msidesc->irq,
thus need to lock the irq descriptor. So I realized we should
rely on arch_setup_msi_irq() to call irq_set_msi_desc():)
Regards!
Gerry

> 
>>
>>> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
>>> ---
>>>  drivers/pci/msi.c |    1 -
>>>  1 file changed, 1 deletion(-)
>>>
>>> diff --git a/drivers/pci/msi.c b/drivers/pci/msi.c
>>> index afe974600c7d..da181c59394b 100644
>>> --- a/drivers/pci/msi.c
>>> +++ b/drivers/pci/msi.c
>>> @@ -685,7 +685,6 @@ static void msix_program_entries(struct pci_dev *dev,
>>>  						PCI_MSIX_ENTRY_VECTOR_CTRL;
>>>  
>>>  		entries[i].vector = entry->irq;
>>> -		irq_set_msi_desc(entry->irq, entry);
>>>  		entry->masked = readl(entry->mask_base + offset);
>>>  		msix_mask_irq(entry, 1);
>>>  		i++;
>>> -- 
>>> 1.7.10.4
>>>
>> --
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>> .
>>
> 
> 
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