linux-kernel - Re: [LKP] [lkp] [x86/hweight] 65ea11ec6a: will-it-scale.per_process

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Date:   Thu, 25 Aug 2016 13:45:06 +0200
From:   Borislav Petkov <bp@...e.de>
To:     "H. Peter Anvin" <hpa@...or.com>
Cc:     "Huang, Ying" <ying.huang@...el.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Brian Gerst <brgerst@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...capital.net>, lkp@...org,
        Thomas Gleixner <tglx@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Ingo Molnar <mingo@...nel.org>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>
Subject: Re: [LKP] [lkp] [x86/hweight] 65ea11ec6a:
 will-it-scale.per_process_ops 9.3% improvement

On Thu, Aug 25, 2016 at 03:05:19AM -0700, H. Peter Anvin wrote:
> I'm wondering if one of those 23 invocations sets up some kind of
> corrupt data that continues to get used.

That could be one plausible explanation. Look at what calls
__sw_hweight64:

initmem_init
numa_policy_init
page_writeback_init
paging_init
pcpu_embed_first_chunk
pcpu_setup_first_chunk
sched_init
set_rq_online.part.46
setup_arch
setup_per_cpu_areas
update_sysctl
x86_64_start_kernel
x86_64_start_reservations
x86_numa_init
zone_sizes_init

I could very well imagine per CPU areas or some sched structure or
whatever getting silently corrupted.

Thanks.

-- 
Regards/Gruss,
    Boris.

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