Re: [Xen-devel] [PATCH v4 2/3] bitmap: import bitmap_{set/clear} from Linux 5.5

From: "Roger Pau Monné" <roger.pau@citrix.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>,
	Julien Grall <julien@xen.org>, Wei Liu <wl@xen.org>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	xen-devel@lists.xenproject.org
Subject: Re: [Xen-devel] [PATCH v4 2/3] bitmap: import bitmap_{set/clear} from Linux 5.5
Date: Fri, 14 Feb 2020 11:40:00 +0100	[thread overview]
Message-ID: <20200214104000.GA4679@Air-de-Roger> (raw)
In-Reply-To: <22c23ea7-e8ee-d09f-6702-888e364f76f0@xen.org>

On Mon, Feb 10, 2020 at 12:54:04PM +0000, Julien Grall wrote:
> 
> 
> On 10/02/2020 12:32, Jan Beulich wrote:
> > On 10.02.2020 13:21, Julien Grall wrote:
> > > Hi,
> > > 
> > > On 10/02/2020 11:59, Jan Beulich wrote:
> > > > On 10.02.2020 12:00, Julien Grall wrote:
> > > > > On 10/02/2020 10:28, Jan Beulich wrote:
> > > > > > On 10.02.2020 10:45, Julien Grall wrote:
> > > > > > > Please suggest a new name for BIT_WORD() and we can repurpose it. So
> > > > > > > far, I have no idea how to rename it.
> > > > > > 
> > > > > > _BIT_WORD() if you/we were to accept the name space violation, or
> > > > > > BITMAP_WORD()?
> > > > > 
> > > > > BITMAP_WORD() is misleading as bitmap are using unsigned long. So my
> > > > > preference is _BIT_WORD().
> > > > > 
> > > > > Another alternative would be ATOMIC_WORD().
> > > > 
> > > > Except that there are also non-atomic bitmap operations, I don't really
> > > > care about the name as long as it's not BIT_WORD() (or anything else
> > > > that's likely to collide with other stuff.
> > > 
> > > I am afraid we are disagreing on what is colliding with what here. The
> > > naming on Arm has been like that for the past few years. While this may
> > > not have been the best choice, this is your suggestion colliding with
> > > what is existing.
> > 
> > It is a plain import from Linux which has turned out impossible
> > because of the change that was done at some point to Arm code
> > which, I guess, also originally came from Linux. There's no new
> > naming I've been suggesting here at all.
> 
> We never claimed we would be fully compatible with Linux and I don't think
> we could every claim it. Particularly, the bitop operations are different
> given Linux bitops are based on unsigned long.
> 
> The bitop did indeed came from Linux originally, however we had to adapt
> them because Linux Armv8 bitop was expecting 8-byte aligned. This does not
> hold on Xen.
> 
> > 
> > > I am not entirely fussed about the namespace violation, although I think
> > > the name is potentially misleading. Yet, I would be happy to use
> > > _BIT_WORD() as this is the best of it so far.
> > > 
> > > While this is code falls under Arm maintainership, I am still happy to
> > > consider other naming. But at this point, you should be the one suggesting.
> > 
> > BIT_UNIT() or BITOP_UNIT() or BITOP_WORD()?
> 
> BITOP_WORD().

So I assume you would like me to import bitmap_{set/clear} and use it
in the x2APIC MSR patch?

Thanks, Roger.

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