From: "H. Peter Anvin" <hpa@zytor.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Eric Dumazet <dada1@cosmosbay.com>,
Davide Libenzi <davidel@xmailserver.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [patch v2] epoll use a single inode ...
Date: Tue, 06 Mar 2007 09:27:20 -0800 [thread overview]
Message-ID: <45EDA478.6060605@zytor.com> (raw)
In-Reply-To: <Pine.LNX.4.64.0703060917500.5963@woody.linux-foundation.org>
Linus Torvalds wrote:
>
> On Tue, 6 Mar 2007, Eric Dumazet wrote:
>> Something like :
>>
>> [PATCH] : Use reciprocal divides in sprintf()
>
> Try this on Core 2, and I suspect that you'll find that the hardware is
> actually *faster* than doing the shift/test, function call and the
> two multiplies.
>
>> Using reciprocal divides permits to change each divide by two multiplies, less
>> expensive on current CPUS.
>
> Are you sure?
>
For base 8 and 16, this is shift and mask, respectively, so it's bound
to be faster (although modern hardware can often optimize this, embedded
hardware definitely can't.) Base 10, which even in the Linux kernel is
almost certainly the most common case, is a lot iffier.
-hpa
next prev parent reply other threads:[~2007-03-06 17:27 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-05 23:41 [patch v2] epoll use a single inode Davide Libenzi
2007-03-06 0:00 ` Linus Torvalds
2007-03-06 0:12 ` Davide Libenzi
2007-03-06 0:20 ` Davide Libenzi
2007-03-06 0:25 ` Linus Torvalds
2007-03-06 2:25 ` H. Peter Anvin
2007-03-06 2:34 ` Davide Libenzi
2007-03-06 2:37 ` H. Peter Anvin
2007-03-06 2:43 ` Davide Libenzi
2007-03-06 6:22 ` Eric Dumazet
2007-03-06 6:31 ` Davide Libenzi
2007-03-06 6:37 ` Davide Libenzi
2007-03-06 16:28 ` H. Peter Anvin
2007-03-06 17:09 ` Linus Torvalds
2007-03-06 17:14 ` H. Peter Anvin
2007-03-06 17:12 ` Eric Dumazet
2007-03-06 17:19 ` Linus Torvalds
2007-03-06 17:27 ` H. Peter Anvin [this message]
2007-03-06 17:28 ` Eric Dumazet
2007-03-06 18:10 ` Eric Dumazet
2007-03-06 20:20 ` Eric Dumazet
2007-03-07 3:47 ` Linus Torvalds
2007-03-07 5:40 ` H. Peter Anvin
2007-03-07 6:57 ` Eric Dumazet
2007-03-07 7:13 ` H. Peter Anvin
2007-03-07 23:46 ` Sami Farin
2007-03-06 18:10 ` Davide Libenzi
2007-03-10 8:06 ` Pavel Machek
2007-03-10 8:24 ` Davide Libenzi
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