linux-kernel - Re: [PATCH v3] arm64: mm: Fix NOMAP page initialization

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Date:   Thu, 12 Jan 2017 16:05:36 +0000
From:   Will Deacon <will.deacon@....com>
To:     Robert Richter <robert.richter@...ium.com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Hanjun Guo <hanjun.guo@...aro.org>,
        Russell King <linux@...linux.org.uk>,
        Catalin Marinas <catalin.marinas@....com>,
        David Daney <david.daney@...ium.com>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v3] arm64: mm: Fix NOMAP page initialization

Hi Robert,

On Mon, Jan 09, 2017 at 12:53:20PM +0100, Robert Richter wrote:
> On 06.01.17 08:37:25, Ard Biesheuvel wrote:
> > Any comments on the performance impact (including boot time) ?
> 
> I did a kernel compile test and kernel mode time increases by about
> 2.2%. Though this is already significant, we need a more suitable mem
> benchmark here for further testing.

Thanks for doing this.

> For boot time I dont see significant changes.
> 
> -Robert
> 
> 
> Boot times:
> 
> pfn_valid_within():
> [   25.929134]
> [   25.548830]
> [   25.503225]
> 
> early_pfn_valid() v3:
> [   25.773814]
> [   25.548428]
> [   25.765290]
> 
> 
> Kernel compile times (3 runs each):
> 
> pfn_valid_within():
> 
> real    6m4.088s
> user    372m57.607s
> sys     16m55.158s
> 
> real    6m1.532s
> user    372m48.453s
> sys     16m50.370s
> 
> real    6m4.061s
> user    373m18.753s
> sys     16m57.027s

Did you reboot the machine between each build here, or only when changing
kernel? If the latter, do you see variations in kernel build time by simply
rebooting the same Image?

Will