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From: David Laight <David.Laight@ACULAB.COM>
To: 'David Daney' <ddaney.cavm@gmail.com>, Christoph Hellwig <hch@lst.de>
Cc: "bhelgaas@google.com" <bhelgaas@google.com>,
	"davem@davemloft.net" <davem@davemloft.net>,
	"netanel@annapurnalabs.com" <netanel@annapurnalabs.com>,
	"jcliburn@gmail.com" <jcliburn@gmail.com>,
	"chris.snook@gmail.com" <chris.snook@gmail.com>,
	"sgoutham@cavium.com" <sgoutham@cavium.com>,
	"rric@kernel.org" <rric@kernel.org>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>
Subject: RE: [PATCH 5/5] PCI: remove pci_enable_msix
Date: Tue, 28 Mar 2017 09:07:28 +0000	[thread overview]
Message-ID: <063D6719AE5E284EB5DD2968C1650D6DCFFBE7F3@AcuExch.aculab.com> (raw)
In-Reply-To: <1eaa46ad-9890-c738-3a85-6468161284ba@gmail.com>

From: David Daney
> Sent: 27 March 2017 18:31
> On 03/27/2017 10:11 AM, Christoph Hellwig wrote:
> > On Mon, Mar 27, 2017 at 09:59:35AM -0700, David Daney wrote:
> >> On 03/27/2017 01:29 AM, Christoph Hellwig wrote:
> >>> Unused now that all callers switched to pci_alloc_irq_vectors.
> >>>
> >>
> >> And you are aware that the ThunderX GPIO driver that I am attempting to
> >> merge uses this interface.
> >>
> >> If this patch gets merged, should I ask to revert it when the GPIO driver
> >> goes in?
> >
> > No.  You should not use pci_enable_msix in your new driver as I told
> > you before.
> >
> >> You offer no solution for drivers that would benefit from using a sparse
> >> sub set of the available MSI-X vectors.
> >
> > Use pci_enable_msix_{exact,range} for now, as I told you before.
> >
> 
> That still results in twice as many MSI-X being provisioned than are needed.
> 
> For drivers that use a contiguous range of MSI-X, your suggestion is
> usable, but for others you are forcing resources to be wasted.  For what
> end?

There are also drivers that only need some interrupts after a specific
device is opened, and could free them when closed.

This could even be network devices with lots of queues, or a driver
realising that the workload is high and per-cpu interrupts make sense.

So any real change to the interface should allow drivers to allocate
and free individual MSI-X vectors.

I remember a lot of discussions when pci_enable_msix_range() was added,
but almost nothing about this change.

	David

  parent reply	other threads:[~2017-03-28  9:07 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-03-27  8:29 remove pci_enable_msix() Christoph Hellwig
2017-03-27  8:29 ` [PATCH 1/5] net: thunderx: switch to pci_alloc_irq_vectors Christoph Hellwig
2017-03-27 16:03   ` Sunil Kovvuri
2017-03-27 17:12     ` Christoph Hellwig
2017-03-27  8:29 ` [PATCH 2/5] net: thunderxvf: " Christoph Hellwig
2017-03-27  8:29 ` [PATCH 3/5] net: alx: " Christoph Hellwig
2017-03-27  8:29 ` [PATCH 4/5] net/ena: " Christoph Hellwig
2017-03-27  8:29 ` [PATCH 5/5] PCI: remove pci_enable_msix Christoph Hellwig
2017-03-27 14:06   ` David Laight
2017-03-27 14:51     ` 'Christoph Hellwig'
2017-03-27 15:03       ` David Laight
2017-03-27 17:10         ` 'Christoph Hellwig'
2017-03-27 16:59   ` David Daney
2017-03-27 17:11     ` Christoph Hellwig
2017-03-27 17:30       ` David Daney
2017-03-28  6:41         ` Christoph Hellwig
2017-03-28 16:24           ` David Daney
2017-03-30 22:56             ` Bjorn Helgaas
2017-03-30 23:00               ` David Daney
2017-03-28  9:07         ` David Laight [this message]
2017-03-30 23:09   ` Bjorn Helgaas

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