linux-kernel - Re: rfc: bool structure members (was Re: [PATCH V3] net/mlx4: Get rid of page operation after dma_alloc

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Message-ID: <20181224231228.GB17036@ziepe.ca>
Date:   Mon, 24 Dec 2018 16:12:28 -0700
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Gal Pressman <galpress@...zon.com>
Cc:     Joe Perches <joe@...ches.com>,
        Bart Van Assche <bvanassche@....org>,
        Stephen Warren <swarren@...dotorg.org>,
        Tariq Toukan <tariqt@...lanox.com>, xavier.huwei@...wei.com,
        netdev@...r.kernel.org, linux-rdma@...r.kernel.org,
        Doug Ledford <dledford@...hat.com>,
        Stephen Warren <swarren@...dia.com>,
        Christoph Hellwig <hch@....de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org
Subject: Re: rfc: bool structure members (was Re: [PATCH V3] net/mlx4: Get
 rid of page operation after dma_alloc_coherent)

On Sun, Dec 23, 2018 at 06:42:20PM +0200, Gal Pressman wrote:
> On 22-Dec-18 01:52, Jason Gunthorpe wrote:
> > On Thu, Dec 20, 2018 at 09:12:43PM -0800, Joe Perches wrote:
> >> Care to submit a coding_style.rst patch or
> >> improve the one below this?
> > 
> > I took yours and revised it a little bit. I spent some time looking at
> > assembly and decided to drop the performance note, the number of cases
> > that run into overhead seems pretty small and probably already
> > requires !! to be correct. There is also an equally unlikely gain, ie
> > 'if (a & b)' optimizes a tiny bit better for bool types.
> > 
> > I also added a small intro on bool, as I know some people are
> > unfamiliar with C11 _Bool and might think bool is just '#define bool
> > u8'
> > 
> > (for those added to the cc) I'm looking at cases, like the patch that
> > spawned this, where the struct has a single bool and no performance
> > considerations. As CH said, seeing that get converted to int due to
> > checkpatch is worse than having used bool. Using u8 won't make this
> > struct smaller or faster.
> > 
> 
> Since a "Using bool" section is added, perhaps it's worth documenting the bool
> usage as a function parameter [1]?
> 
> [1] https://www.spinics.net/lists/linux-rdma/msg72336.html

I'm not really sure how to express that as something concrete.. That
specific case clearly called out for a flags as it was a widely used
API - maybe less spread out cases like static functions or something
are OK??

Jason