Subject: Re: [PATCH] dma-mapping: Reduce dma_mapping_error() inline bloat
To: Robin Murphy <robin.murphy@arm.com>, hch@lst.de
Cc: linux-kernel@vger.kernel.org
From: Marek Szyprowski <m.szyprowski@samsung.com>
Message-id: <200b5187-e162-2bc3-7c04-268ae4fcbd61@samsung.com>
Date: Tue, 01 Aug 2017 09:58:07 +0200
User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101
        Thunderbird/52.2.1
MIME-version: 1.0
In-reply-to: <6a23eacf6603e75e995f8720c24b54c4fc2926f5.1500917215.git.robin.murphy@arm.com>
Content-type: text/plain; charset=utf-8; format=flowed
Content-transfer-encoding: 7bit
Content-language: en-US
CMS-TYPE: 201P
References: <CGME20170724172940epcas4p4b06b8fd5c66a475e1f8be1361981a14b@epcas4p4.samsung.com>
 <6a23eacf6603e75e995f8720c24b54c4fc2926f5.1500917215.git.robin.murphy@arm.com>
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1757
Lines: 49

Hi Robin,

On 2017-07-24 19:29, Robin Murphy wrote:
> Thanks to the nested inlining, all drivers correctly calling
> dma_mapping_error() after a mapping a page or single buffer generate two
> calls to get_arch_dma_ops() per callsite, which all adds up to a fair
> old chunk of useless code, e.g. ~3KB for an arm64 defconfig plus extras:
>
>     text	   data	    bss	    dec	    hex	filename
> 13051391	1503898	 327768	14883057	 e318f1	vmlinux.o.old
> 13050751	1503898	 327768	14882417	 e31671	vmlinux.o.new
>
> Give the compiler a hand by making it clear we want the same ops.

Reviewed-by: Marek Szyprowski <m.szyprowski@samsung.com>

Similar pattern is used in drivers/xen/swiotlb-xen.c for mmap and
get_sgtable. This could be also fixed, although those are not used so
frequently as dma_mapping_error.

> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>   include/linux/dma-mapping.h | 7 ++++---
>   1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index 843ab866e0f4..239e53d12ee8 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -541,10 +541,11 @@ static inline void dma_free_noncoherent(struct device *dev, size_t size,
>   
>   static inline int dma_mapping_error(struct device *dev, dma_addr_t dma_addr)
>   {
> -	debug_dma_mapping_error(dev, dma_addr);
> +	const struct dma_map_ops *ops = get_dma_ops(dev);
>   
> -	if (get_dma_ops(dev)->mapping_error)
> -		return get_dma_ops(dev)->mapping_error(dev, dma_addr);
> +	debug_dma_mapping_error(dev, dma_addr);
> +	if (ops->mapping_error)
> +		return ops->mapping_error(dev, dma_addr);
>   	return 0;
>   }
>   

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland