From: Jason Gunthorpe <jgg@ziepe•ca>
To: Joe Perches <joe@perches•com>
Cc: Bart Van Assche <bvanassche@acm•org>,
Stephen Warren <swarren@wwwdotorg•org>,
Tariq Toukan <tariqt@mellanox•com>,
xavier.huwei@huawei•com, netdev@vger•kernel.org,
linux-rdma@vger•kernel.org, Doug Ledford <dledford@redhat•com>,
Stephen Warren <swarren@nvidia•com>,
Christoph Hellwig <hch@lst•de>,
Andrew Morton <akpm@linux-foundation•org>,
Linus Torvalds <torvalds@linux-foundation•org>
Subject: Re: rfc: bool structure members (was Re: [PATCH V3] net/mlx4: Get rid of page operation after dma_alloc_coherent)
Date: Thu, 20 Dec 2018 20:31:59 -0700 [thread overview]
Message-ID: <20181221033159.GF23877@ziepe.ca> (raw)
In-Reply-To: <072c2d9d187daf0672bf54ab035e47a05fd1cd1d.camel@perches.com>
On Thu, Dec 20, 2018 at 06:25:05PM -0800, Joe Perches wrote:
> I agree it's not a very good message nor is bool use
> of structure members a real problem except in very
> few cases.
I think the issue is that the link it shows lacks the context of the
discussion thread - and the actual guidance here is more
complicated.
A discussion in coding style would probably be better.
- Don't put multiple true/false fields in a single struct (be it bool,
u8, int, etc) - use bit-fields instead.
- Don't use bool if cache line layout matters, its size and alignment
varies
- Do use bool to clearly express that the variable, parameter or
structure member can only take on a true/false value.
.. and I also seem to remember there is a small performance downside
to bool stores in some ABIs as the compiler has to cannonize stores to
0 or 1? But this also eliminates certain bug classes..
Jason
next prev parent reply other threads:[~2018-12-21 3:32 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-19 18:20 [PATCH V3] net/mlx4: Get rid of page operation after dma_alloc_coherent Stephen Warren
2018-12-20 17:43 ` Jason Gunthorpe
2018-12-20 17:44 ` Christoph Hellwig
2018-12-20 17:49 ` Bart Van Assche
2018-12-21 2:25 ` rfc: bool structure members (was Re: [PATCH V3] net/mlx4: Get rid of page operation after dma_alloc_coherent) Joe Perches
2018-12-21 2:40 ` Andrew Morton
2018-12-21 3:31 ` Jason Gunthorpe [this message]
2018-12-21 5:12 ` Joe Perches
2018-12-21 23:52 ` Jason Gunthorpe
2018-12-23 16:42 ` Gal Pressman
2018-12-23 16:53 ` Al Viro
2018-12-24 22:08 ` Jason Gunthorpe
2018-12-24 23:12 ` Jason Gunthorpe
2018-12-25 8:41 ` Gal Pressman
2019-01-02 16:29 ` [PATCH V3] net/mlx4: Get rid of page operation after dma_alloc_coherent Stephen Warren
2019-01-03 7:48 ` Christoph Hellwig
2019-01-03 14:32 ` Tariq Toukan
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