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Subject: Re: RFC: Petition Intel/AMD to add POPF_IF insn
To: Linus Torvalds <torvalds@linux-foundation.org>
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Cc: Andy Lutomirski <luto@amacapital.net>,
        Sara Sharon <sara.sharon@intel.com>,
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        Johannes Berg <johannes.berg@intel.com>,
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From: Denys Vlasenko <dvlasenk@redhat.com>
Message-ID: <f7123992-8173-67fc-b79f-bebc98abb123@redhat.com>
Date: Thu, 18 Aug 2016 19:49:10 +0200
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On 08/18/2016 07:47 PM, Denys Vlasenko wrote:
> On 08/18/2016 07:24 PM, Linus Torvalds wrote:
>> That said, your numbers really aren't very convincing. If popf really
>> is just 10 cycles on modern Intel hardware, it's already fast enough
>> that I really don't think it matters.
>
> It's 20 cycles. I was wrong in my email, I forgot that the insn count
> also counts "push %ebx" insns.
>
> Since I already made a mistake, let me double-check.
>
> 200 million iterations of this loop execute under 17 seconds:
>
>   400100:    b8 00 c2 eb 0b           mov    $0xbebc200,%eax # 1000*1000*1000

Grr. It's 200*1000*1000, not one billion. Sorry.