From: Robin Murphy <robin.murphy@arm.com>
To: Christoph Hellwig <hch@lst.de>
Cc: iommu@lists.linux-foundation.org,
Marek Szyprowski <m.szyprowski@samsung.com>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 2/5] dma-direct: add an explicit dma_direct_get_required_mask
Date: Thu, 27 Sep 2018 16:35:21 +0100 [thread overview]
Message-ID: <d9ce1c62-9e89-dc73-68e8-4e3025b5725f@arm.com> (raw)
In-Reply-To: <20180927152818.GC10566@lst.de>
On 27/09/18 16:28, Christoph Hellwig wrote:
> On Thu, Sep 27, 2018 at 03:12:25PM +0100, Robin Murphy wrote:
>>> +u64 dma_direct_get_required_mask(struct device *dev)
>>> +{
>>> + u64 max_dma = phys_to_dma_direct(dev, (max_pfn - 1) << PAGE_SHIFT);
>>> +
>>> + return (1ULL << (fls64(max_dma) - 1)) * 2 - 1;
>>
>> I think that may as well just use __fls64() - it seems reasonable to assume
>> max_dma > 0. Otherwise,
>
> Is there any good reason to micro-optimize given that this isn't
> a fast path?
Not at all, I wasn't even thinking in terms of optimisation other than
in terms of number of source characters and levels of parentheses.
But more importantly I was also being a big idiot because no matter how
much I have the fls()/__fls() thing in mind, __fls64() doesn't actually
exist. Nitpick rescinded!
Robin.
WARNING: multiple messages have this Message-ID (diff)
From: Robin Murphy <robin.murphy-5wv7dgnIgG8@public.gmane.org>
To: Christoph Hellwig <hch-jcswGhMUV9g@public.gmane.org>
Cc: Benjamin Herrenschmidt
<benh-XVmvHMARGAS8U2dJNN8I7kB+6BGkLq7r@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org,
Greg Kroah-Hartman
<gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org>,
linuxppc-dev-uLR06cmDAlY/bJ5BZ2RsiQ@public.gmane.org
Subject: Re: [PATCH 2/5] dma-direct: add an explicit dma_direct_get_required_mask
Date: Thu, 27 Sep 2018 16:35:21 +0100 [thread overview]
Message-ID: <d9ce1c62-9e89-dc73-68e8-4e3025b5725f@arm.com> (raw)
In-Reply-To: <20180927152818.GC10566-jcswGhMUV9g@public.gmane.org>
On 27/09/18 16:28, Christoph Hellwig wrote:
> On Thu, Sep 27, 2018 at 03:12:25PM +0100, Robin Murphy wrote:
>>> +u64 dma_direct_get_required_mask(struct device *dev)
>>> +{
>>> + u64 max_dma = phys_to_dma_direct(dev, (max_pfn - 1) << PAGE_SHIFT);
>>> +
>>> + return (1ULL << (fls64(max_dma) - 1)) * 2 - 1;
>>
>> I think that may as well just use __fls64() - it seems reasonable to assume
>> max_dma > 0. Otherwise,
>
> Is there any good reason to micro-optimize given that this isn't
> a fast path?
Not at all, I wasn't even thinking in terms of optimisation other than
in terms of number of source characters and levels of parentheses.
But more importantly I was also being a big idiot because no matter how
much I have the fls()/__fls() thing in mind, __fls64() doesn't actually
exist. Nitpick rescinded!
Robin.
next prev parent reply other threads:[~2018-09-27 15:35 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-20 18:52 dma mask related fixups (including full bus_dma_mask support) Christoph Hellwig
2018-09-20 18:52 ` [PATCH 1/5] dma-mapping: make the get_required_mask method available unconditionally Christoph Hellwig
2018-09-27 1:28 ` Benjamin Herrenschmidt
2018-09-27 1:28 ` Benjamin Herrenschmidt
2018-09-20 18:52 ` [PATCH 2/5] dma-direct: add an explicit dma_direct_get_required_mask Christoph Hellwig
2018-09-27 1:31 ` Benjamin Herrenschmidt
2018-09-27 1:31 ` Benjamin Herrenschmidt
2018-09-27 14:12 ` Robin Murphy
2018-09-27 15:28 ` Christoph Hellwig
2018-09-27 15:35 ` Robin Murphy [this message]
2018-09-27 15:35 ` Robin Murphy
2018-09-20 18:52 ` [PATCH 3/5] dma-direct: refine dma_direct_alloc zone selection Christoph Hellwig
2018-09-27 1:45 ` Benjamin Herrenschmidt
2018-09-27 1:45 ` Benjamin Herrenschmidt
2018-09-27 13:49 ` Christoph Hellwig
2018-09-27 13:49 ` Christoph Hellwig
2018-09-28 0:06 ` Benjamin Herrenschmidt
2018-09-28 0:06 ` Benjamin Herrenschmidt
2018-09-28 0:06 ` Benjamin Herrenschmidt
2018-09-28 15:46 ` Christoph Hellwig
2018-09-28 15:46 ` Christoph Hellwig
2018-09-27 14:30 ` Robin Murphy
2018-09-27 15:30 ` Christoph Hellwig
2018-09-27 15:38 ` Robin Murphy
2018-09-27 15:38 ` Robin Murphy
2018-09-27 15:41 ` Christoph Hellwig
2018-09-27 15:41 ` Christoph Hellwig
2018-09-20 18:52 ` [PATCH 4/5] dma-direct: implement complete bus_dma_mask handling Christoph Hellwig
2018-09-27 14:58 ` Robin Murphy
2018-09-27 14:58 ` Robin Murphy
2018-09-27 15:32 ` Christoph Hellwig
2018-09-27 16:14 ` Robin Murphy
2018-09-27 16:14 ` Robin Murphy
2018-09-27 16:27 ` Christoph Hellwig
2018-09-27 16:27 ` Christoph Hellwig
2018-09-27 16:27 ` Christoph Hellwig
2018-09-27 16:41 ` Robin Murphy
2018-09-27 16:41 ` Robin Murphy
2018-09-27 16:41 ` Robin Murphy
2018-09-20 18:52 ` [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size Christoph Hellwig
2018-09-27 1:50 ` Benjamin Herrenschmidt
2018-09-27 1:50 ` Benjamin Herrenschmidt
2018-09-27 13:49 ` Christoph Hellwig
2018-09-27 15:07 ` Robin Murphy
2018-09-27 22:35 dma mask related fixups (including full bus_dma_mask support) v2 Christoph Hellwig
2018-09-27 22:35 ` [PATCH 2/5] dma-direct: add an explicit dma_direct_get_required_mask Christoph Hellwig
2018-09-27 22:35 ` Christoph Hellwig
2018-09-27 22:35 ` Christoph Hellwig
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=d9ce1c62-9e89-dc73-68e8-4e3025b5725f@arm.com \
--to=robin.murphy@arm.com \
--cc=benh@kernel.crashing.org \
--cc=gregkh@linuxfoundation.org \
--cc=hch@lst.de \
--cc=iommu@lists.linux-foundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=m.szyprowski@samsung.com \
/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 an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.