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Subject: Re: [PATCH v2] dmadev: fix structure alignment
To: Wenwu Ma <wenwux.ma@intel.com>, <dev@dpdk.org>
CC: <songx.jiale@intel.com>, <stable@dpdk.org>
References: <20240308053711.1260154-1-wenwux.ma@intel.com>
<20240315014331.1376720-1-wenwux.ma@intel.com>
From: fengchengwen <fengchengwen@huawei.com>
Message-ID: <096d2161-026c-f89e-c44b-340a3148bccc@huawei.com>
Date: Fri, 15 Mar 2024 14:06:07 +0800
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Hi Wenwu,
On 2024/3/15 9:43, Wenwu Ma wrote:
> The structure rte_dma_dev needs only 8 byte alignment.
> This patch replaces __rte_cache_aligned of rte_dma_dev
> with __rte_aligned(8).
>
> Fixes: b36970f2e13e ("dmadev: introduce DMA device library")
> Cc: stable@dpdk.org
>
> Signed-off-by: Wenwu Ma <wenwux.ma@intel.com>
> ---
> v2:
> - Because of performance drop, adjust the code to
> no longer demand cache line alignment
Which two versions observed performance drop? And which benchmark observed drop?
Could you provide more information?
>
> ---
> lib/dmadev/rte_dmadev_pmd.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/dmadev/rte_dmadev_pmd.h b/lib/dmadev/rte_dmadev_pmd.h
> index 58729088ff..b569bb3502 100644
> --- a/lib/dmadev/rte_dmadev_pmd.h
> +++ b/lib/dmadev/rte_dmadev_pmd.h
> @@ -122,7 +122,7 @@ enum rte_dma_dev_state {
> * @internal
> * The generic data structure associated with each DMA device.
> */
> -struct __rte_cache_aligned rte_dma_dev {
> +struct __rte_aligned(8) rte_dma_dev {
The DMA fast-path was implemented by struct rte_dma_fp_objs, which is not
rte_dma_dev? So why is it a problem here?
Thanks
> /** Device info which supplied during device initialization. */
> struct rte_device *device;
> struct rte_dma_dev_data *data; /**< Pointer to shared device data. */
>