From: Arnd Bergmann <arnd@arndb.de>
To: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 1/5] bitops: add generic implementation of ext2 atomic bitops by test_and_{set,clear}_bit
Date: Sun, 10 Oct 2010 18:36:52 +0200 [thread overview]
Message-ID: <201010101836.52406.arnd@arndb.de> (raw)
In-Reply-To: <AANLkTikjb8aTBoXm3+9ULQDB9OvdxwHcQ=BSS4aBJm9i@mail.gmail.com>
On Sunday 10 October 2010 17:07:26 Akinobu Mita wrote:
> Some architectures use spinlock to implement it
> (asm-generic/bitops/ext2-atomic.h). Most other architectures use
> test_and_set_bit() and test_and_clear_bit() as this patch shows.
>
> Why are there two implementations? test_and_{set,clear}_bit() are more
> costly operations than spinlock for some architectures?
I would guess that is only true on architectures that implement all atomics
using a hashed spinlock like cris, sparc32 or parisc. This way the user
can decide which spinlock to use rather than have the arch code calculate
a hash on the pointer.
This is an ext2 specific micro-optimization that I don't think makes
sense in the generic le bitops code.
Arnd
next prev parent reply other threads:[~2010-10-10 16:37 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-08 10:03 [PATCH 1/5] bitops: add generic implementation of ext2 atomic bitops by test_and_{set,clear}_bit Akinobu Mita
2010-10-08 10:03 ` [PATCH 2/5] bitops: cleanup asm-generic/bitops/le.h Akinobu Mita
2010-10-08 10:03 ` [PATCH 3/5] kvm: stop including asm-generic/bitops/le.h directly Akinobu Mita
2010-10-08 12:45 ` Alexander Graf
2010-10-08 10:03 ` [PATCH 4/5] rds: " Akinobu Mita
2010-10-08 18:55 ` Andy Grover
2010-10-08 18:59 ` David Miller
2010-10-10 15:09 ` Akinobu Mita
2010-10-08 10:03 ` [PATCH 5/5] bitops: forbid asm-generic/bitops/le.h direct inclusion Akinobu Mita
2010-10-08 10:24 ` [PATCH 1/5] bitops: add generic implementation of ext2 atomic bitops by test_and_{set,clear}_bit Christoph Hellwig
2010-10-10 15:07 ` Akinobu Mita
2010-10-10 16:36 ` Arnd Bergmann [this message]
2010-10-12 3:39 ` Akinobu Mita
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=201010101836.52406.arnd@arndb.de \
--to=arnd@arndb.de \
--cc=akinobu.mita@gmail.com \
--cc=akpm@linux-foundation.org \
--cc=hch@infradead.org \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.