From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
netdev@vger.kernel.org, axboe@kernel.dk, kvalo@codeaurora.org,
john.johansen@canonical.com, linux-arch@vger.kernel.org
Subject: Re: [PATCH] unaligned: delete 1-byte accessors
Date: Mon, 22 Jul 2019 14:48:46 +0900 [thread overview]
Message-ID: <1563774526.3223.2.camel@HansenPartnership.com> (raw)
In-Reply-To: <20190722052244.GA4235@avx2>
On Mon, 2019-07-22 at 08:22 +0300, Alexey Dobriyan wrote:
> On Mon, Jul 22, 2019 at 08:08:33AM +0900, James Bottomley wrote:
> > On Mon, 2019-07-22 at 00:52 +0300, Alexey Dobriyan wrote:
> > > Each and every 1-byte access is aligned!
> >
> > The design idea of this is for parsing descriptors. We simply
> > chunk up the describing structure using get_unaligned for
> > everything. The reason is because a lot of these structures come
> > with reserved areas which we may make use of later. If we're using
> > get_unaligned for everything we can simply change a u8 to a u16 in
> > the structure absorbing the reserved padding. With your change now
> > I'd have to chase down every byte access and replace it with
> > get_unaligned instead of simply changing the structure.
> >
> > What's the significant advantage of this change that compensates
> > for the problems the above causes?
>
> HW descriptors have fixed endianness, you're supposed to use
> get_unaligned_be32() and friends.
Not if this is an internal descriptor format, which is what this is
mostly used for.
> For that matter, drivers/scsi/ has exactly 2 get_unaligned() calls
> one of which can be changed to get_unaligned_be32().
You haven't answered the "what is the benefit of this change" question.
I mean sure we can do it, but it won't make anything more efficient
and it does help with the descriptor format to treat every structure
field the same.
James
next prev parent reply other threads:[~2019-07-22 5:49 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-21 21:52 [PATCH] unaligned: delete 1-byte accessors Alexey Dobriyan
2019-07-21 23:08 ` James Bottomley
2019-07-22 5:22 ` Alexey Dobriyan
2019-07-22 5:48 ` James Bottomley [this message]
2019-07-22 6:07 ` Alexey Dobriyan
2019-07-22 6:20 ` James Bottomley
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