From: Michael Ellerman <michael@ellerman.id.au>
To: Tejun Heo <tj@kernel.org>
Cc: Alexander Gordeev <agordeev@redhat.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.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: Tue, 1 Oct 2013 17:26:43 +1000 [thread overview]
Message-ID: <20131001072642.GH17966@concordia> (raw)
In-Reply-To: <20130920122603.GC7630@mtj.dyndns.org>
On Fri, Sep 20, 2013 at 07:26:03AM -0500, Tejun Heo wrote:
> Hello,
>
> On Wed, Sep 18, 2013 at 06:50:45PM +0200, Alexander Gordeev wrote:
> > Actually, I do not see much contradiction with what I proposed. The
> > key words here "determine the number of MSIs the controller wants".
> >
> > In general case it is not what pci_msix_table_size() returns (or at
> > least we should not limit ourselves to it) - there could be non-
> > standard means to report number of MSIs: hardcoded, version-dependant,
> > device-specific registers etc.
> >
> > Next, if we opt to determine the number of MSIs by non-MSI standard
> > means then there is no reason not to call pci_get_msix_limit() (or
> > whatever) at this step.
>
> Yeah, that's all fine. My point is that we shouldn't try to use
> "degraded" multiple MSI mode where the number of MSIs allocated is
> smaller than performing full multiple MSI operation. How that number
> is determined doesn't really matter but that number is a property
> which is solely decided by the device driver, right? If a device
> needs full multiple MSI mode, given specific configuration, it needs
> >= X number of MSIs and that's the number it should request.
Sure, the driver is in full control. If it can ONLY work with N MSIs
then it should try for N, else fallback to 1.
But some drivers are able to work with a range of values for N, and
performance is improved vs using a single MSI.
> > Being Captain Obvious here, but it is up to the device driver to handle
> > a failure. There could be no such option as single MSI mode after all :)
>
> I don't think there actually is a mainstream device which can't
> fallback to single interrupt. Anyways, the point is the same, let's
> please not try to create an interface which encourages complex retry
> logic in its users which are likely to involve less traveled and
> tested paths in both the driver and firmware.
Why support > 1 MSI at all? It just adds complex logic and less travelled
paths in the driver and firmware.
cheers
next prev parent reply other threads:[~2013-10-01 7:26 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 [this message]
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
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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