From: Michael Ellerman <michael@ellerman.id.au>
To: Alexander Gordeev <agordeev@redhat.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Tejun Heo <tj@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
"linux-ide@vger.kernel.org" <linux-ide@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>, Joerg Roedel <joro@8bytes.org>,
Jan Beulich <JBeulich@suse.com>,
Bjorn Helgaas <bhelgaas@google.com>,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi_cap() interface
Date: Wed, 2 Oct 2013 12:43:24 +1000 [thread overview]
Message-ID: <20131002024324.GC22748@concordia> (raw)
In-Reply-To: <20131001103526.GA5053@dhcp-26-207.brq.redhat.com>
On Tue, Oct 01, 2013 at 12:35:27PM +0200, Alexander Gordeev wrote:
> On Tue, Oct 01, 2013 at 05:51:33PM +1000, Michael Ellerman wrote:
> > The disadvantage is that any restriction imposed on us above the quota
> > can only be reported as an error from pci_enable_msix().
> >
> > The quota code, called from pci_get_msix_limit(), can only do so much to
> > interogate firmware about the limitations. The ultimate way to check if
> > firmware will give us enough MSIs is to try and allocate them. But we
> > can't do that from pci_get_msix_limit() because the driver is not asking
> > us to enable MSIs, just query them.
>
> If things are this way then pci_enable_msix() already exposed to this
> problem internally on pSeries.
>
> I see that even successful quota checks in rtas_msi_check_device() and
> rtas_setup_msi_irqs() do not guarantee (as you say) that firmware will
> give enough MSIs. Hence, pci_enable_msix() might fail even though the
> its quota checks succeeded.
Yes, but it can report that failure to the caller, which can then retry.
> Therefore, nothing will really change if we make pci_get_msix_limit() check
> quota and hope the follow-up call to pci_enable_msix() succeeded.
No that's not equivalent. Under your scheme if pci_enable_msix() fails
then the caller just bails, it will never try again with a lower number.
> (Of course, we could allocate-deallocate MSIs at check time, but I think it
> is an overkill).
It's not only overkill, it's messing with the device behind the drivers
back, which is definitely a no-no in my opinion.
> > You'll also need to add another arch hook, for the quota check, and
> > we'll have to add it to our per-platform indirection as well.
>
> Already, in a branch, hidden from Bjorn & Tejun eyes ;)
>
> > All a lot of bother for no real gain IMHO.
>
> Well, I do not have a strong opinion here. I leave it to the ones who have :)
> But few drivers have became clearer as result of this change (and messy ones
> are still messy).
Amen.
cheers
next prev parent reply other threads:[~2013-10-02 2:43 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-05 12:51 [PATCH v2 0/6] AHCI: Conserve interrupts with pci_enable_msi_block_part() interface Alexander Gordeev
2013-09-05 12:52 ` [PATCH v2 1/6] PCI/MSI: Introduce " Alexander Gordeev
2013-09-05 12:52 ` [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi_cap() interface Alexander Gordeev
2013-09-05 13:09 ` Tejun Heo
2013-09-05 15:03 ` Alexander Gordeev
2013-09-05 15:04 ` Tejun Heo
2013-09-05 15:40 ` Alexander Gordeev
2013-09-05 15:44 ` Tejun Heo
2013-09-05 18:54 ` Alexander Gordeev
2013-09-05 20:06 ` Tejun Heo
2013-09-06 16:01 ` Bjorn Helgaas
2013-09-06 16:06 ` Tejun Heo
2013-09-06 23:32 ` Bjorn Helgaas
2013-09-09 15:20 ` Alexander Gordeev
2013-09-09 15:22 ` [PATCH 1/9] PCI/MSI/PPC: Fix wrong RTAS error code reporting Alexander Gordeev
2013-09-09 15:22 ` [PATCH 2/9] PCI/MSI/PPC: Make return values only 0/-errno when MSIs allocated Alexander Gordeev
2013-09-09 15:24 ` [PATCH 3/9] PCI/MSI/x86: " Alexander Gordeev
2013-09-09 15:24 ` [PATCH 4/9] PCI/MSI/MIPS: " Alexander Gordeev
2013-09-09 15:25 ` [PATCH 2/9] PCI/MSI/PPC: Make return values only 0/-errno when MSIs allocated[PATCH 5/9] PCI/MSI/s390: " Alexander Gordeev
2013-09-09 15:38 ` scrap this one Alexander Gordeev
2013-09-09 15:26 ` [PATCH 5/9] PCI/MSI/s390: Make return values only 0/-errno when MSIs allocated Alexander Gordeev
2013-09-10 12:42 ` Sergei Shtylyov
2013-09-10 13:09 ` Alexander Gordeev
2013-09-09 15:27 ` [PATCH 6/9] PCI/MSI/s390: Remove superfluous check of MSI type Alexander Gordeev
2013-09-09 15:28 ` [PATCH 7/9] PCI/MSI/s390: Make return values only 0/-errno when MSIs allocated Alexander Gordeev
2013-09-09 15:29 ` [PATCH 8/9] PCI/MSI: Fix return value when populate_msi_sysfs() failed Alexander Gordeev
2013-09-09 15:29 ` [PATCH 9/9] PCI/MSI: Make return values only 0/-errno when MSIs allocated Alexander Gordeev
2013-09-09 15:37 ` [PATCH v2 2/6] PCI/MSI: Factor out pci_get_msi_cap() interface Tejun Heo
2013-09-09 15:45 ` Alexander Gordeev
2013-09-16 10:22 ` Alexander Gordeev
2013-09-17 14:30 ` Michael Ellerman
2013-09-18 9:48 ` Alexander Gordeev
2013-09-18 14:22 ` Tejun Heo
2013-09-18 16:50 ` Alexander Gordeev
2013-09-20 8:24 ` Alexander Gordeev
2013-09-20 12:27 ` Tejun Heo
2013-09-25 18:02 ` Bjorn Helgaas
2013-09-25 20:58 ` Alexander Gordeev
2013-09-25 21:00 ` Tejun Heo
2013-09-26 7:46 ` Alexander Gordeev
2013-09-26 8:58 ` David Laight
2013-09-26 10:45 ` Alexander Gordeev
2013-09-26 11:34 ` David Laight
2013-09-26 12:13 ` Alexander Gordeev
2013-09-26 13:11 ` Tejun Heo
2013-09-26 14:39 ` Alexander Gordeev
2013-09-26 14:42 ` Tejun Heo
2013-10-01 7:19 ` Michael Ellerman
2013-09-20 12:26 ` Tejun Heo
2013-10-01 7:26 ` Michael Ellerman
2013-10-01 7:35 ` Michael Ellerman
2013-10-01 11:55 ` Tejun Heo
2013-10-02 2:33 ` Michael Ellerman
2013-10-02 3:23 ` Tejun Heo
2013-09-26 12:32 ` Mark Lord
2013-09-26 13:03 ` Alexander Gordeev
2013-10-02 2:46 ` Mark Lord
2013-10-02 7:26 ` Alexander Gordeev
2013-12-18 18:26 ` Bjorn Helgaas
2013-10-01 7:51 ` Michael Ellerman
2013-10-01 10:35 ` Alexander Gordeev
2013-10-02 2:43 ` Michael Ellerman [this message]
2013-10-02 7:10 ` Alexander Gordeev
2013-09-06 13:17 ` Alexander Gordeev
2013-09-05 12:53 ` [PATCH v2 3/6] MSI/x86: Support pci_enable_msi_block_part() interface Alexander Gordeev
2013-09-05 12:53 ` [PATCH v2 4/6] AHCI: Conserve interrupts with " Alexander Gordeev
2013-09-05 13:10 ` Tejun Heo
2013-09-05 15:23 ` Alexander Gordeev
2013-09-05 12:54 ` [PATCH v2 5/6] AHCI: Check MRSM bit when multiple MSIs enabled Alexander Gordeev
2013-09-05 13:11 ` Tejun Heo
2013-09-05 15:25 ` Alexander Gordeev
2013-09-05 14:32 ` Sergei Shtylyov
2013-09-05 12:54 ` [PATCH v2 6/6] PCI/MSI: Get rid of pci_enable_msi_block_auto() interface Alexander Gordeev
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