From: Eric Biggers <ebiggers@kernel.org>
To: "Matthew Wilcox (Oracle)" <willy@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Hannes Reinecke <hare@suse.de>,
Luis Chamberlain <mcgrof@kernel.org>,
Pankaj Raghav <p.raghav@samsung.com>,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v2 7/7] buffer: Fix more functions for block size > PAGE_SIZE
Date: Thu, 9 Nov 2023 20:50:19 -0800 [thread overview]
Message-ID: <20231110045019.GB6572@sol.localdomain> (raw)
In-Reply-To: <20231109210608.2252323-8-willy@infradead.org>
On Thu, Nov 09, 2023 at 09:06:08PM +0000, Matthew Wilcox (Oracle) wrote:
> Replace the shift with a divide, which is probably cheaper than first
> calculating the shift.
No. The divs are almost certainly more expensive on most CPUs, especially when
doing two of them. On x86_64 for example, it will be two div instructions
instead of one bsr and two shr instructions. The two divs are much more costly.
The block size is always a power of 2; we should take advantage of that.
- Eric
next prev parent reply other threads:[~2023-11-10 4:50 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-09 21:06 [PATCH v2 0/7] More buffer_head cleanups Matthew Wilcox (Oracle)
2023-11-09 21:06 ` [PATCH v2 1/7] buffer: Return bool from grow_dev_folio() Matthew Wilcox (Oracle)
2023-11-10 3:43 ` Ryusuke Konishi
2023-12-30 9:23 ` Matthew Wilcox
2023-12-30 12:22 ` Ryusuke Konishi
2023-11-09 21:06 ` [PATCH v2 2/7] buffer: Calculate block number inside folio_init_buffers() Matthew Wilcox (Oracle)
2023-11-09 21:06 ` [PATCH v2 3/7] buffer: Fix grow_buffers() for block size > PAGE_SIZE Matthew Wilcox (Oracle)
2023-11-10 6:37 ` Ryusuke Konishi
2023-11-10 11:29 ` Ryusuke Konishi
2023-11-10 13:23 ` Matthew Wilcox
2023-11-12 4:52 ` kernel test robot
2023-11-13 17:10 ` Andrew Morton
2023-11-13 17:20 ` Nathan Chancellor
2023-11-15 11:14 ` Naresh Kamboju
2023-11-09 21:06 ` [PATCH v2 4/7] buffer: Cast block to loff_t before shifting it Matthew Wilcox (Oracle)
2023-11-09 21:06 ` [PATCH v2 5/7] buffer: Fix various functions for block size > PAGE_SIZE Matthew Wilcox (Oracle)
2023-11-10 7:48 ` Ryusuke Konishi
2023-11-10 13:36 ` Matthew Wilcox
2023-11-10 15:23 ` Ryusuke Konishi
2023-11-09 21:06 ` [PATCH v2 6/7] buffer: Handle large folios in __block_write_begin_int() Matthew Wilcox (Oracle)
2023-11-09 21:06 ` [PATCH v2 7/7] buffer: Fix more functions for block size > PAGE_SIZE Matthew Wilcox (Oracle)
2023-11-10 4:50 ` Eric Biggers [this message]
2023-11-10 14:26 ` Matthew Wilcox
2023-11-11 18:06 ` Eric Biggers
2023-11-12 4:52 ` Matthew Wilcox
2023-11-12 6:00 ` Eric Biggers
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