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Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM

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On 19/07/2017 18:13, Radim Krčmář wrote:
> Good point, 'select' seems misused here.
> 
> There is no reason to depend on TASKSTATS (nor NET+MULTIUSER), we only
> suggest to enable it with KVM.  KVM uses sched_info_on() to handle any
> any possible resulting configuration, c9aaa8957f20 ("KVM: Steal time
> implementation").
> 
> KVM would work as intended if 'select' would not enable the option if
> its dependencies failed (instead of unconditionally forcing the option).
> 
> Is the preferred way to encode it:
> 
>   'default y if KVM' in config TASK_DELAY_ACCT
>   (that adds a non-local and enigmatic dependency and also needlessly
>    expands the possible configuration space)
> 
> or
> 
>   'select TASKSTATS if NET && MULTIUSER' in config KVM
>   (that is going to break when dependencies of TASKSTATS change again)
> 
> ?

I think the former is the closest to what the user actually wants, and
it would let us clean up arch/x86/kvm/Kconfig.  However it should be
"default y if KVM && X86'.

Maybe there is room for a new operator "suggest Y" which, when added
inside "config X", operates as if "config Y" had a "default y if X".

In this case, kvm could do

-	depends on NET && MULTIUSER
-	select TASKSTATS
+	suggest TASKSTATS

Thanks,

Paolo

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[PATCH 0/8] x86: randconfig warning fixes Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
  [PATCH 3/8] x86: math-emu: avoid bogus -Wint-in-bool-context warning Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
    [tip:x86/urgent] x86/fpu/math-emu: Avoid bogus  -Wint-in-bool-context warning tip-bot for Arnd Bergmann <tipbot@zytor.com> - 2017-07-20 12:30 +0200
  [PATCH 5/8] x86: silence build with "make -s" Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
    [tip:x86/urgent] x86/build: Silence the build with "make -s" tip-bot for Arnd Bergmann <tipbot@zytor.com> - 2017-07-20 12:40 +0200
  [PATCH 6/8] x86: add MULTIUSER dependency for KVM Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
    Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM Radim Krčmář <rkrcmar@redhat.com> - 2017-07-19 16:20 +0200
      Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM Arnd Bergmann <arnd@arndb.de> - 2017-07-19 16:20 +0200
        Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM Radim Krčmář <rkrcmar@redhat.com> - 2017-07-19 18:20 +0200
          Re: [PATCH 6/8] x86: add MULTIUSER dependency for KVM Paolo Bonzini <pbonzini@redhat.com> - 2017-07-23 15:50 +0200
  [PATCH 2/8] x86: math-emu: possible uninitialized variable use Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
    [tip:x86/urgent] x86/fpu/math-emu: Fix possible uninitialized  variable use tip-bot for Arnd Bergmann <tipbot@zytor.com> - 2017-07-20 12:30 +0200
  [PATCH 1/8] perf/x86: shut up false-positive -Wmaybe-uninitialized warning Arnd Bergmann <arnd@arndb.de> - 2017-07-19 15:00 +0200
    [tip:x86/urgent] perf/x86: Shut up false-positive  -Wmaybe-uninitialized warning tip-bot for Arnd Bergmann <tipbot@zytor.com> - 2017-07-20 12:30 +0200

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