From: "H. Peter Anvin" <hpa@zytor.com>
To: Maksym Planeta <mcsim.planeta@gmail.com>
Cc: mingo@redhat.com, kernel-janitors@vger.kernel.org,
namhyung@gmail.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] x86: page: get_order() optimization
Date: Mon, 28 Mar 2011 12:47:57 -0700 [thread overview]
Message-ID: <4D90E5ED.3080604@zytor.com> (raw)
In-Reply-To: <1301215556-8898-1-git-send-email-mcsim.planeta@gmail.com>
On 03/27/2011 01:45 AM, Maksym Planeta wrote:
> For x86 architecture get_order function can be optimized due to
> assembler instruction bsr.
>
> This is second version of patch where for constants gcc precompute the
> result.
>
> Signed-off-by: Maksym Planeta <mcsim.planeta@gmail.com>
gcc 4.x has an intrinsic, __builtin_clz(), which does the opposite of
the bsr instruction; specifically:
__builtin_clz(x) ^ 31
... generates a bsrl instruction if x is variable. This tends to
generate much better code than any assembly hacks.
-hpa
next prev parent reply other threads:[~2011-03-28 19:48 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-03-27 8:45 [PATCH v2] x86: page: get_order() optimization Maksym Planeta
2011-03-27 11:33 ` Ingo Molnar
2011-03-27 16:22 ` Peter Hüwe
2011-03-27 17:15 ` Maksym Planeta
2011-03-28 5:08 ` Ingo Molnar
2011-03-28 19:33 ` Maksym Planeta
2011-03-28 19:44 ` H. Peter Anvin
2011-04-01 14:08 ` Maksym Planeta
2011-03-28 19:47 ` H. Peter Anvin [this message]
2011-03-29 7:27 ` Ingo Molnar
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