linux-kernel - Re: [PATCH 1/2] perf_event: remove unused DEBUG_PERF_USE

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Message-ID: <20160831070457.GY10138@twins.programming.kicks-ass.net>
Date:   Wed, 31 Aug 2016 09:04:57 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kim Phillips <kim.phillips@....com>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Johannes Weiner <hannes@...xchg.org>,
        Arnd Bergmann <arnd@...db.de>, Tejun Heo <tj@...nel.org>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linuxppc-dev@...ts.ozlabs.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 1/2] perf_event: remove unused DEBUG_PERF_USE_VMALLOC

On Tue, Aug 30, 2016 at 02:08:34PM -0500, Kim Phillips wrote:
> This 'DEBUG'-prefixed version of PERF_USE_VMALLOC is not used anywhere.
> It appears to be leftovers from commit 906010b "perf_event: Provide
> vmalloc() based mmap() backing" that introduced it.
> 
> Not sure what commit cb30711 "perf_event: Don't allow vmalloc() backed
> perf on powerpc" was trying to do with it either.
> 
> Signed-off-by: Kim Phillips <kim.phillips@....com>
> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> ---
>  init/Kconfig | 13 -------------
>  1 file changed, 13 deletions(-)
> 
> diff --git a/init/Kconfig b/init/Kconfig
> index cac3f09..934a61f 100644
> --- a/init/Kconfig
> +++ b/init/Kconfig
> @@ -1707,19 +1707,6 @@ config PERF_EVENTS
>  
>  	  Say Y if unsure.
>  
> -config DEBUG_PERF_USE_VMALLOC
> -	default n
> -	bool "Debug: use vmalloc to back perf mmap() buffers"
> -	depends on PERF_EVENTS && DEBUG_KERNEL && !PPC
> -	select PERF_USE_VMALLOC

^^^^^


It forces the use of vmalloc backed pages for the ring-buffer so that we
can test that code on x86, which otherwise doesn't use it.