From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To: Robin Murphy <robin.murphy@arm.com>, Leon Romanovsky <leon@kernel.org>
Cc: andrew.murray@arm.com, maz@kernel.org,
linux-kernel@vger.kernel.org,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Hanjun Guo <guohanjun@huawei.com>,
Sudeep Holla <sudeep.holla@arm.com>,
Tariq Toukan <tariqt@mellanox.com>,
Rob Herring <robh+dt@kernel.org>,
Frank Rowand <frowand.list@gmail.com>,
Shawn Lin <shawn.lin@rock-chips.com>,
Heiko Stuebner <heiko@sntech.de>, Christoph Hellwig <hch@lst.de>,
Marek Szyprowski <m.szyprowski@samsung.com>,
james.quinlan@broadcom.com, mbrugger@suse.com,
f.fainelli@gmail.com, phil@raspberrypi.org, wahrenst@gmx.net,
jeremy.linton@arm.com, linux-pci@vger.kernel.org,
linux-rpi-kernel@lists.infradead.org,
"Rafael J. Wysocki" <rjw@rjwysocki.net>,
Len Brown <lenb@kernel.org>,
"David S. Miller" <davem@davemloft.net>,
Bjorn Helgaas <bhelgaas@google.com>,
linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
netdev@vger.kernel.org, linux-rdma@vger.kernel.org,
devicetree@vger.kernel.org, linux-rockchip@lists.infradead.org,
iommu@lists.linux-foundation.org
Subject: Re: [PATCH v3 1/7] linux/log2.h: Add roundup/rounddown_pow_two64() family of functions
Date: Wed, 27 Nov 2019 19:24:07 +0100 [thread overview]
Message-ID: <b30002d48c9d010a1ee81c16cd29beee914c3b1d.camel@suse.de> (raw)
In-Reply-To: <6e0b9079-9efd-2884-26d1-3db2d622079d@arm.com>
[-- Attachment #1: Type: text/plain, Size: 2096 bytes --]
On Wed, 2019-11-27 at 18:06 +0000, Robin Murphy wrote:
> On 26/11/2019 12:51 pm, Leon Romanovsky wrote:
> > On Tue, Nov 26, 2019 at 10:19:39AM +0100, Nicolas Saenz Julienne wrote:
> > > Some users need to make sure their rounding function accepts and returns
> > > 64bit long variables regardless of the architecture. Sadly
> > > roundup/rounddown_pow_two() takes and returns unsigned longs. Create a
> > > new generic 64bit variant of the function and cleanup rougue custom
> > > implementations.
> >
> > Is it possible to create general roundup/rounddown_pow_two() which will
> > work correctly for any type of variables, instead of creating special
> > variant for every type?
>
> In fact, that is sort of the case already - roundup_pow_of_two() itself
> wraps ilog2() such that the constant case *is* type-independent. And
> since ilog2() handles non-constant values anyway, might it be reasonable
> to just take the strongly-typed __roundup_pow_of_two() helper out of the
> loop as below?
>
> Robin
>
That looks way better that's for sure. Some questions.
> ----->8-----
> diff --git a/include/linux/log2.h b/include/linux/log2.h
> index 83a4a3ca3e8a..e825f8a6e8b5 100644
> --- a/include/linux/log2.h
> +++ b/include/linux/log2.h
> @@ -172,11 +172,8 @@ unsigned long __rounddown_pow_of_two(unsigned long n)
> */
> #define roundup_pow_of_two(n) \
> ( \
> - __builtin_constant_p(n) ? ( \
> - (n == 1) ? 1 : \
> - (1UL << (ilog2((n) - 1) + 1)) \
> - ) : \
> - __roundup_pow_of_two(n) \
> + (__builtin_constant_p(n) && (n == 1)) ? \
> + 1 : (1UL << (ilog2((n) - 1) + 1)) \
Then here you'd have to use ULL instead of UL, right? I want my 64bit value
everywhere regardless of the CPU arch. The downside is that would affect
performance to some extent (i.e. returning a 64bit value where you used to have
a 32bit one)?
Also, what about callers to this function on platforms with 32bit 'unsigned
longs' that happen to input a 64bit value into this. IIUC we'd have a change of
behaviour.
Regards,
Nicolas
[-- Attachment #2: This is a digitally signed message part --]
[-- Type: application/pgp-signature, Size: 488 bytes --]
next prev parent reply other threads:[~2019-11-27 18:24 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-26 9:19 [PATCH v3 0/7] Raspberry Pi 4 PCIe support Nicolas Saenz Julienne
2019-11-26 9:19 ` [PATCH v3 1/7] linux/log2.h: Add roundup/rounddown_pow_two64() family of functions Nicolas Saenz Julienne
2019-11-26 12:51 ` Leon Romanovsky
2019-11-27 18:06 ` Robin Murphy
2019-11-27 18:24 ` Nicolas Saenz Julienne [this message]
2019-11-27 19:06 ` Robin Murphy
2019-11-27 19:12 ` Leon Romanovsky
2019-11-27 19:16 ` Nicolas Saenz Julienne
2019-11-27 17:36 ` Nicolas Saenz Julienne
2019-11-26 21:50 ` [PATCH v3 0/7] Raspberry Pi 4 PCIe support Bjorn Helgaas
2019-11-27 17:28 ` Nicolas Saenz Julienne
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=b30002d48c9d010a1ee81c16cd29beee914c3b1d.camel@suse.de \
--to=nsaenzjulienne@suse.de \
--cc=andrew.murray@arm.com \
--cc=bhelgaas@google.com \
--cc=davem@davemloft.net \
--cc=devicetree@vger.kernel.org \
--cc=f.fainelli@gmail.com \
--cc=frowand.list@gmail.com \
--cc=guohanjun@huawei.com \
--cc=hch@lst.de \
--cc=heiko@sntech.de \
--cc=iommu@lists.linux-foundation.org \
--cc=james.quinlan@broadcom.com \
--cc=jeremy.linton@arm.com \
--cc=lenb@kernel.org \
--cc=leon@kernel.org \
--cc=linux-acpi@vger.kernel.org \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-pci@vger.kernel.org \
--cc=linux-rdma@vger.kernel.org \
--cc=linux-rockchip@lists.infradead.org \
--cc=linux-rpi-kernel@lists.infradead.org \
--cc=lorenzo.pieralisi@arm.com \
--cc=m.szyprowski@samsung.com \
--cc=maz@kernel.org \
--cc=mbrugger@suse.com \
--cc=netdev@vger.kernel.org \
--cc=phil@raspberrypi.org \
--cc=rjw@rjwysocki.net \
--cc=robh+dt@kernel.org \
--cc=robin.murphy@arm.com \
--cc=shawn.lin@rock-chips.com \
--cc=sudeep.holla@arm.com \
--cc=tariqt@mellanox.com \
--cc=wahrenst@gmx.net \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).