linux-kernel - Re: [PATCH v2 2/2] dma: add IOMMU static calls with clear default ops

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Message-ID: <20240729140736.GC5669@unreal>
Date: Mon, 29 Jul 2024 17:07:36 +0300
From: Leon Romanovsky <leon@...nel.org>
To: Mostafa Saleh <smostafa@...gle.com>
Cc: Christoph Hellwig <hch@....de>, Robin Murphy <robin.murphy@....com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Easwar Hariharan <eahariha@...ux.microsoft.com>,
	linux-kernel@...r.kernel.org, iommu@...ts.linux.dev,
	Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v2 2/2] dma: add IOMMU static calls with clear default ops

On Mon, Jul 29, 2024 at 12:41:12PM +0000, Mostafa Saleh wrote:
> Hi Leon,
> 
> On Wed, Jul 17, 2024 at 03:37:11PM +0300, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@...dia.com>
> > 
> > Most of the arch DMA ops (which often, but not  always, involve
> > some sort of IOMMU) are using the same DMA operations. These DMA
> > operations are default ones implemented in drivers/iomem/dma-iommu.c.
> > 
> > So let's make sure to call them directly without need to perform function
> > pointers dereference.
> 
> Just out of curiosity, is there any observed improvement from that?
> As from my experience the DMA-IOMMU path is quite dense so it won't
> be senstive to such micro-optimizations.

DMA-IOMMU no, but NVMe driver which uses DMA-API in datapath will
potentially benefit from this change.

I personally used this change to simplify my "DMA split ... " series [1].

[1] https://git.kernel.org/pub/scm/linux/kernel/git/leon/linux-rdma.git/log/?h=dma-split-v2

Thanks