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Message-ID: <CAObL_7FUDpV9md+UnDbXxWw=trrXLFLNNJMNegdezrQt7rm6TA@mail.gmail.com>
Date: Mon, 21 Apr 2014 18:06:19 -0700
From: Andrew Lutomirski <amluto@...il.com>
To: "H. Peter Anvin" <hpa@...or.com>
Cc: "H. Peter Anvin" <hpa@...ux.intel.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
Ingo Molnar <mingo@...nel.org>,
Alexander van Heukelum <heukelum@...tmail.fm>,
Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
Borislav Petkov <bp@...en8.de>,
Arjan van de Ven <arjan.van.de.ven@...el.com>,
Brian Gerst <brgerst@...il.com>,
Alexandre Julliard <julliard@...ehq.com>,
Andi Kleen <andi@...stfloor.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86-64: espfix for 64-bit mode *PROTOTYPE*
On Mon, Apr 21, 2014 at 5:53 PM, H. Peter Anvin <hpa@...or.com> wrote:
> Well, if 2^17 CPUs are allocated we might 2K pages allocated. We could easily do a bitmap here, of course. NR_CPUS/64 is a small number, and would reduce the code complexity.
>
Even simpler: just get rid of the check entirely. That is, break out
of the higher level loops once one of them is set (this should be a
big speedup regardless) and don't allocate the page if the first PTE
is already pointing at something.
After all, espfix_already_there is mostly a duplicate of init_espfix_cpu.
--Andy
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