From: Dave Hansen <dave@linux.vnet.ibm.com>
To: Jesse Gross <jesse@nicira.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org,
David Rientjes <rientjes@google.com>
Subject: Re: [PATCH] flex_array: Avoid divisions when accessing elements.
Date: Wed, 27 Apr 2011 09:13:39 -0700 [thread overview]
Message-ID: <1303920819.9308.19723.camel@nimitz> (raw)
In-Reply-To: <1303850501-16249-1-git-send-email-jesse@nicira.com>
On Tue, 2011-04-26 at 13:41 -0700, Jesse Gross wrote:
> On most architectures division is an expensive operation and
> accessing an element currently requires four of them. This
> performance penalty effectively precludes flex arrays from
> being used on any kind of fast path. However, two of these
> divisions can be handled at creation time and the others can
> be replaced by a reciprocal divide, completely avoiding real
> divisions on access.
flex_array.c has a nice table for how many objects can be allocated:
* Element size | Objects | Objects |
* PAGE_SIZE=4k | 32-bit | 64-bit |
* ---------------------------------|
* 1 bytes | 4186112 | 2093056 |
* 2 bytes | 2093056 | 1046528 |
* 3 bytes | 1395030 | 697515 |
* 4 bytes | 1046528 | 523264 |
* 32 bytes | 130816 | 65408 |
* 33 bytes | 126728 | 63364 |
* 2048 bytes | 2044 | 1022 |
* 2049 bytes | 1022 | 511 |
* void * | 1046528 | 261632 |
This patch changes that a bit. Would you mind updating it?
-- Dave
next prev parent reply other threads:[~2011-04-27 16:14 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-26 20:41 [PATCH] flex_array: Avoid divisions when accessing elements Jesse Gross
2011-04-27 16:13 ` Dave Hansen [this message]
2011-04-29 1:48 ` Jesse Gross
-- strict thread matches above, loose matches on Subject: below --
2011-05-02 17:26 [PATCH] flex_array: avoid " Eric Paris
2011-05-02 17:36 ` Dave Hansen
2011-05-02 20:23 ` Jesse Gross
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1303920819.9308.19723.camel@nimitz \
--to=dave@linux.vnet.ibm.com \
--cc=akpm@linux-foundation.org \
--cc=jesse@nicira.com \
--cc=linux-kernel@vger.kernel.org \
--cc=rientjes@google.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox