Message-ID: <553E8C3E.8040701@redhat.com>
Date: Mon, 27 Apr 2015 21:21:34 +0200
From: Denys Vlasenko <dvlasenk@redhat.com>
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To: Borislav Petkov <bp@alien8.de>,
        Linus Torvalds <torvalds@linux-foundation.org>
CC: Andy Lutomirski <luto@amacapital.net>, Andy Lutomirski <luto@kernel.org>,
        X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        Denys Vlasenko <vda.linux@googlemail.com>,
        Brian Gerst <brgerst@gmail.com>, Ingo Molnar <mingo@kernel.org>,
        Steven Rostedt <rostedt@goodmis.org>, Oleg Nesterov <oleg@redhat.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Alexei Starovoitov <ast@plumgrid.com>, Will Drewry <wad@chromium.org>,
        Kees Cook <keescook@chromium.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] x86_64, asm: Work around AMD SYSRET SS descriptor attribute
 issue
References: <20150425211206.GE32099@pd.tnic> <CALCETrWvqyCYOzCYXz7ZnzaM0obbidqo5CxVp2Hn1ELEiC3m3g@mail.gmail.com> <20150427085305.GB6774@pd.tnic> <20150427113506.GG6774@pd.tnic> <CA+55aFykNBrdHFSVeLftG7Ujx4Tk=MuUJXD2rNYn9kwL+kLN5w@mail.gmail.com> <20150427154631.GB28871@pd.tnic> <CA+55aFxWyhc+ax_jnqH9zsvqruL63gcePMbRQGJ_wM06e1QKpA@mail.gmail.com> <20150427164024.GD28871@pd.tnic> <CA+55aFySbPjeCgetxeSQPSP-h+yKnrHPcTGuoorAHJbCj53-8A@mail.gmail.com> <20150427183854.GG28871@pd.tnic> <20150427191145.GJ28871@pd.tnic>
In-Reply-To: <20150427191145.GJ28871@pd.tnic>
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On 04/27/2015 09:11 PM, Borislav Petkov wrote:
> A:     709.528485252 seconds time elapsed                                          ( +-  0.02% )
> B:     708.976557288 seconds time elapsed                                          ( +-  0.04% )
> C:     709.312844791 seconds time elapsed                                          ( +-  0.02% )
> D:     709.400050112 seconds time elapsed                                          ( +-  0.01% )
> E:     708.914562508 seconds time elapsed                                          ( +-  0.06% )
> F:     709.602255085 seconds time elapsed                                          ( +-  0.02% )

That's about 0.2% variance. Very small.

Sounds obvious, but. Did you try running a test several times?
Maybe you are measuring random noise.


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