From: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
To: Alexander Gordeev <agordeev@redhat.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org,
linux-pci@vger.kernel.org,
Suresh Siddha <suresh.b.siddha@intel.com>,
Yinghai Lu <yinghai@kernel.org>, Joerg Roedel <joro@8bytes.org>,
Jan Beulich <JBeulich@suse.com>, Ingo Molnar <mingo@redhat.com>,
Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: [PATCH v3 -tip x86/apic 1/2] PCI/MSI: Allocate as many multiple-MSIs as requested
Date: Wed, 5 Jun 2013 22:56:38 +0200 [thread overview]
Message-ID: <20130605205638.GA5816@breakpoint.cc> (raw)
In-Reply-To: <8575dc590b819892f366852fe50835efaf579f4f.1368431413.git.agordeev@redhat.com>
On Mon, May 13, 2013 at 11:05:48AM +0200, Alexander Gordeev wrote:
> Note, although the existing 'msi_desc::multiple' field might seem
> redundant, in fact in does not. In general case the number of MSIs a
> PCI device is initialized with is not necessarily the closest power-
> of-two value of the number of MSIs the device will send. Thus, in
> theory it would not be always possible to derive the former from the
> latter and we need to keep them both, to stress this corner case.
> Besides, since 'msi_desc::multiple' is a bitfield, throwing it out
> would not save us any space.
The last paragraph makes me curious. The only place where 'multiple' is set is
in do_setup_msi_irqs() and this uses the next power of two for it. And since a
device is not enabled twice, it is not overridden.
So it should be possible to compute 'multiple' out of 'nvec' but it saves
cycles not do to so. I agree to keep 'multiple' but your argument does not
seem to make sense.
While nitpicking, 'nvec' might deserve a better comment than 'number of
messages' since it holds the number of allocated interrupts. :)
Sebastian
next prev parent reply other threads:[~2013-06-05 20:57 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-05-13 9:05 [PATCH v3 -tip x86/apic 0/2] PCI/MSI: Allocate as many multiple-MSIs as requested Alexander Gordeev
2013-05-13 9:05 ` [PATCH v3 -tip x86/apic 1/2] " Alexander Gordeev
2013-05-28 9:50 ` Ingo Molnar
2013-06-05 20:56 ` Sebastian Andrzej Siewior [this message]
2013-06-05 21:09 ` Bjorn Helgaas
2013-06-05 21:28 ` Sebastian Andrzej Siewior
2013-06-06 8:30 ` Alexander Gordeev
2013-06-06 19:51 ` Sebastian Andrzej Siewior
2013-05-13 9:06 ` [PATCH v3 -tip x86/apic 2/2] x86/MSI: Conserve interrupt resources when using multiple-MSIs Alexander Gordeev
2013-06-05 20:08 ` Sebastian Andrzej Siewior
2013-05-28 21:51 [PATCH v3 -tip x86/apic 1/2] PCI/MSI: Allocate as many multiple-MSIs as requested Bjorn Helgaas
2013-05-29 8:36 ` Alexander Gordeev
2013-05-29 20:58 ` Bjorn Helgaas
2013-06-03 20:46 ` Bjorn Helgaas
2013-06-04 13:14 ` Alexander Gordeev
2013-06-05 17:18 ` Bjorn Helgaas
2013-06-05 18:33 ` Konrad Rzeszutek Wilk
2013-06-05 18:35 ` Bjorn Helgaas
2013-06-20 12:51 ` Joerg Roedel
2013-06-25 17:34 ` Bjorn Helgaas
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