Re: [PATCH v1 1/2] x86: kconfig: remove X86_UP_IOAPIC

[David Rientjes]

On Wed, 11 Mar 2015, Luis R. Rodriguez wrote:

> From: "Luis R. Rodriguez" <mcgrof@xxxxxxxx>
> 
> X86_UP_IOAPIC is a way so that 32-bit UP systems can enable
> X86_IOAPIC. X86_UP_IOAPIC is only as a visible user option if
> you are on a 32-bit system but have X86_UP_APIC enabled. X86_UP_APIC
> will be enabled by force if you have PCI_MSI on 32-bit systems
> now, X86_UP_APIC will now only be user selectable if you didn't
> have PCI_MSI enabled and are also not on a X86_32_NON_STANDARD
> system. Bryan's original patch (refactored commit log in commit
> 38a1dfda) [0] describes that Intel CE, Intel MID and Intel Quark
> are all 32-bit uniprocessor systems with IO-APICs, the code change
> however only *re-enabled* UP_IOAPIC as an *option* when PCI_MSI
> was enabled, but given that:
> 
> 1) enabling X86_IOAPIC is the real end goal here
> 2) enabling X86_IOAPIC only increases the kernel only by 12064 bytes (~12 KiB)
> 3) enabling X86_IOAPIC will in no way slow down your kernel
> 
> Let's make a compromise for 32-bit systems and always enable X86_IOAPIC
> when X86_UP_IOAPIC is enabled as 32-bit systems are not in a state
> of flux and the price for the size is small with no performance impact.
> 
> Using:
> 
> export ARCH=i386
> make allnoconfig
> --> Enabling PCI_MSI
> make localyesconfig
> 
> With X86_IO_APIC:
> mcgrof@ergon ~/linux-next (git::master)$ du -b arch/x86/boot/bzImage
> 734608  arch/x86/boot/bzImage
> 
> Without X86_IO_APIC:
> mcgrof@ergon ~/linux-next (git::master)$ du -b arch/x86/boot/bzImage
> 722544  arch/x86/boot/bzImage
> 

1.6% increase.

> [0] https://lkml.org/lkml/2015/1/22/718
> 
> Cc: David Rientjes <rientjes@xxxxxxxxxx>
> Cc: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
> Cc: Bryan O'Donoghue <pure.logic@xxxxxxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> Cc: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxx>
> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> Cc: Jan Beulich <JBeulich@xxxxxxxx>
> Cc: Juergen Gross <jgross@xxxxxxxx>
> Cc: linux-pci@xxxxxxxxxxxxxxx
> Cc: x86@xxxxxxxxxx
> Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxx>
> ---
>  arch/x86/Kconfig | 15 ++-------------
>  1 file changed, 2 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 110f6ae..b17a8ea 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -899,6 +899,7 @@ config X86_UP_APIC
>  	bool "Local APIC support on uniprocessors" if !PCI_MSI
>  	default PCI_MSI
>  	depends on X86_32 && !SMP && !X86_32_NON_STANDARD
> +	select X86_IO_APIC
>  	---help---
>  	  A local APIC (Advanced Programmable Interrupt Controller) is an
>  	  integrated interrupt controller in the CPU. If you have a single-CPU
> @@ -909,18 +910,6 @@ config X86_UP_APIC
>  	  performance counters), and the NMI watchdog which detects hard
>  	  lockups.
>  
> -config X86_UP_IOAPIC
> -	bool "IO-APIC support on uniprocessors"
> -	depends on X86_UP_APIC
> -	---help---
> -	  An IO-APIC (I/O Advanced Programmable Interrupt Controller) is an
> -	  SMP-capable replacement for PC-style interrupt controllers. Most
> -	  SMP systems and many recent uniprocessor systems have one.
> -
> -	  If you have a single-CPU system with an IO-APIC, you can say Y here
> -	  to use it. If you say Y here even though your machine doesn't have
> -	  an IO-APIC, then the kernel will still run with no slowdown at all.
> -
>  config X86_LOCAL_APIC
>  	def_bool y
>  	depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
> @@ -928,7 +917,7 @@ config X86_LOCAL_APIC
>  
>  config X86_IO_APIC
>  	def_bool y
> -	depends on X86_LOCAL_APIC || X86_UP_IOAPIC
> +	depends on X86_LOCAL_APIC
>  	select IRQ_DOMAIN
>  
>  config X86_REROUTE_FOR_BROKEN_BOOT_IRQS

I think it would be best to remove the "select" so the "depends" for both 
config options won't diverge in the future.  This should be equivalent, 
right?

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -909,18 +909,6 @@ config X86_UP_APIC
 	  performance counters), and the NMI watchdog which detects hard
 	  lockups.
 
-config X86_UP_IOAPIC
-	bool "IO-APIC support on uniprocessors"
-	depends on X86_UP_APIC
-	---help---
-	  An IO-APIC (I/O Advanced Programmable Interrupt Controller) is an
-	  SMP-capable replacement for PC-style interrupt controllers. Most
-	  SMP systems and many recent uniprocessor systems have one.
-
-	  If you have a single-CPU system with an IO-APIC, you can say Y here
-	  to use it. If you say Y here even though your machine doesn't have
-	  an IO-APIC, then the kernel will still run with no slowdown at all.
-
 config X86_LOCAL_APIC
 	def_bool y
 	depends on X86_64 || SMP || X86_32_NON_STANDARD || X86_UP_APIC || PCI_MSI
@@ -928,7 +916,7 @@ config X86_LOCAL_APIC
 
 config X86_IO_APIC
 	def_bool y
-	depends on X86_LOCAL_APIC || X86_UP_IOAPIC
+	depends on X86_LOCAL_APIC || X86_UP_APIC
 	select IRQ_DOMAIN
 
 config X86_REROUTE_FOR_BROKEN_BOOT_IRQS

And then the second patch adds a 3.8% increase on top of this (and the two 
"select" statements in that patch shouldn't be necessary, both 
X86_LOCAL_APIC and X86_IO_APIC are def_bool y for PCI_MSI configs).  If 
these are just cleanup patches, I'm not sure I understand why a 
considerable kernel text size increase is worth it.
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