From: David Sterba <dsterba@suse.cz>
To: Johannes Thumshirn <Johannes.Thumshirn@wdc.com>
Cc: Qu Wenruo <quwenruo.btrfs@gmx.com>,
David Sterba <dsterba@suse.com>,
"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH 01/10] btrfs: use precalculated sectorsize_bits from fs_info
Date: Mon, 2 Nov 2020 16:08:51 +0100 [thread overview]
Message-ID: <20201102150851.GD6756@twin.jikos.cz> (raw)
In-Reply-To: <SN4PR0401MB3598B9DAD09F08946CBF6C3E9B100@SN4PR0401MB3598.namprd04.prod.outlook.com>
On Mon, Nov 02, 2020 at 02:31:35PM +0000, Johannes Thumshirn wrote:
> On 02/11/2020 15:20, Qu Wenruo wrote:
> > This may sounds like a nitpicking, but what about "ffs(4096) - 1"?
> > IMHO it should be a little more faster than ilog2, especially when we
> > have ensure all sector size is power of 2 already.
>
> Looking at the actual ilog2() implementation (and considering you're
> passing 4096, a constant) you'll end up in const_ilog() which will
> evaluate to 9.
>
> ffs() on the other hand on x86_64 will evaluate to a bfsl. So ffs() will
> evaluated at runtime, while ilog2() at compile time.
As the value is calculated only once for the whole filesystem lifetime,
I'm not concerned about speed but readability.
next prev parent reply other threads:[~2020-11-02 15:10 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-29 14:27 [PATCH 00/10] Sectorsize, csum_size lifted to fs_info David Sterba
2020-10-29 14:27 ` [PATCH 01/10] btrfs: use precalculated sectorsize_bits from fs_info David Sterba
2020-11-02 14:05 ` Qu Wenruo
2020-11-02 14:18 ` Qu Wenruo
2020-11-02 14:31 ` Johannes Thumshirn
2020-11-02 15:08 ` David Sterba [this message]
2020-11-02 15:12 ` Johannes Thumshirn
2020-11-02 15:15 ` David Sterba
2020-11-03 9:31 ` David Sterba
2020-10-29 14:27 ` [PATCH 02/10] btrfs: replace div_u64 by shift in free_space_bitmap_size David Sterba
2020-11-02 14:07 ` Qu Wenruo
2020-10-29 14:27 ` [PATCH 03/10] btrfs: replace s_blocksize_bits with fs_info::sectorsize_bits David Sterba
2020-11-02 14:23 ` Qu Wenruo
2020-11-02 15:18 ` David Sterba
2020-10-29 14:27 ` [PATCH 04/10] btrfs: store precalculated csum_size in fs_info David Sterba
2020-10-29 14:27 ` [PATCH 05/10] btrfs: precalculate checksums per leaf once David Sterba
2020-11-02 14:27 ` Qu Wenruo
2020-11-02 15:24 ` David Sterba
2020-11-02 16:00 ` David Sterba
2020-10-29 14:27 ` [PATCH 06/10] btrfs: use cached value of fs_info::csum_size everywhere David Sterba
2020-11-02 14:28 ` Qu Wenruo
2020-10-29 14:27 ` [PATCH 07/10] btrfs: switch cached fs_info::csum_size from u16 to u32 David Sterba
2020-10-29 14:27 ` [PATCH 08/10] btrfs: remove unnecessary local variables for checksum size David Sterba
2020-10-29 14:43 ` Johannes Thumshirn
2020-10-29 14:27 ` [PATCH 09/10] btrfs: check integrity: remove local copy of csum_size David Sterba
2020-10-29 14:44 ` Johannes Thumshirn
2020-10-29 14:27 ` [PATCH 10/10] btrfs: scrub: remove local copy of csum_size from context David Sterba
2020-10-29 14:45 ` Johannes Thumshirn
2020-10-29 14:54 ` David Sterba
2020-10-29 15:01 ` Johannes Thumshirn
2020-10-29 14:50 ` [PATCH 00/10] Sectorsize, csum_size lifted to fs_info Johannes Thumshirn
2020-10-29 16:25 ` David Sterba
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=20201102150851.GD6756@twin.jikos.cz \
--to=dsterba@suse.cz \
--cc=Johannes.Thumshirn@wdc.com \
--cc=dsterba@suse.com \
--cc=linux-btrfs@vger.kernel.org \
--cc=quwenruo.btrfs@gmx.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;
as well as URLs for NNTP newsgroup(s).