linux-kernel - Re: RFC: Petition Intel/AMD to add POPF

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Date:   Thu, 18 Aug 2016 19:22:16 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Denys Vlasenko <dvlasenk@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Sara Sharon <sara.sharon@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Christian König <christian.koenig@....com>,
        Vinod Koul <vinod.koul@...el.com>,
        Alex Deucher <alexander.deucher@....com>,
        Johannes Berg <johannes.berg@...el.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Andy Lutomirski <luto@...nel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: RFC: Petition Intel/AMD to add POPF_IF insn



On 18/08/2016 14:18, Denys Vlasenko wrote:
> 
> -     2,588,839,023      branches                  #  977.555
> M/sec                    ( +-  0.02% )
> +     2,599,319,615      branches                  # 1046.786
> M/sec                    ( +-  0.04% )
> -         3,620,273      branch-misses             #    0.14% of all
> branches          ( +-  0.67% )
> +         3,577,771      branch-misses             #    0.14% of all
> branches          ( +-  0.69% )
> -       2.648799072 seconds time
> elapsed                                          ( +-  0.24% )
> +       2.487452268 seconds time
> elapsed                                          ( +-  0.31% )
> 
> Good, we run more insns/cycle, as expected. However, a bit more branches.

Can you see where the missed branches are?  Assuming branch misses are
the case where IF=0, perhaps there are a few places that can be changed
to spin_lock/unlock_irq or local_irq_disable/enable.

Paolo