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From: John Garry via iommu <iommu@lists.linux-foundation.org>
To: Robin Murphy <robin.murphy@arm.com>,
	<damien.lemoal@opensource.wdc.com>, <joro@8bytes.org>,
	<will@kernel.org>, <jejb@linux.ibm.com>,
	<martin.petersen@oracle.com>, <hch@lst.de>,
	<m.szyprowski@samsung.com>
Cc: linux-scsi@vger.kernel.org, linux-doc@vger.kernel.org,
	linuxarm@huawei.com, iommu@lists.linux.dev,
	linux-kernel@vger.kernel.org, linux-ide@vger.kernel.org,
	iommu@lists.linux-foundation.org
Subject: Re: [PATCH v4 1/5] dma-mapping: Add dma_opt_mapping_size()
Date: Tue, 28 Jun 2022 12:27:38 +0100	[thread overview]
Message-ID: <a2e717d0-c3e2-ea98-9d8b-cee1fd37c117@huawei.com> (raw)
In-Reply-To: <bbca5df5-8681-d6d9-201d-3d48b34e3001@arm.com>

On 28/06/2022 12:23, Robin Murphy wrote:
>> +
>> +    size_t
>> +    dma_opt_mapping_size(struct device *dev);
>> +
>> +Returns the maximum optimal size of a mapping for the device. Mapping 
>> large
>> +buffers may take longer so device drivers are advised to limit total DMA
>> +streaming mappings length to the returned value.
> 
> Nit: I'm not sure "advised" is necessarily the right thing to say in 
> general - that's only really true for a caller who cares about 
> throughput of churning through short-lived mappings more than anything 
> else, and doesn't take a significant hit overall from splitting up 
> larger requests. I do think it's good to clarify the exact context of 
> "optimal" here, but I'd prefer to be objectively clear that it's for 
> workloads where the up-front mapping overhead dominates.

Ok, sure, I can make that clear.

Thanks,
John
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WARNING: multiple messages have this Message-ID (diff)
From: John Garry <john.garry@huawei.com>
To: Robin Murphy <robin.murphy@arm.com>,
	<damien.lemoal@opensource.wdc.com>, <joro@8bytes.org>,
	<will@kernel.org>, <jejb@linux.ibm.com>,
	<martin.petersen@oracle.com>, <hch@lst.de>,
	<m.szyprowski@samsung.com>
Cc: <linux-doc@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
	<linux-ide@vger.kernel.org>, <iommu@lists.linux-foundation.org>,
	<iommu@lists.linux.dev>, <linux-scsi@vger.kernel.org>,
	<linuxarm@huawei.com>
Subject: Re: [PATCH v4 1/5] dma-mapping: Add dma_opt_mapping_size()
Date: Tue, 28 Jun 2022 12:27:38 +0100	[thread overview]
Message-ID: <a2e717d0-c3e2-ea98-9d8b-cee1fd37c117@huawei.com> (raw)
Message-ID: <20220628112738.Ku7IYxMmW_JnoVItD9NAnA7ijdaQFjU9Dc3sLPRbwY4@z> (raw)
In-Reply-To: <bbca5df5-8681-d6d9-201d-3d48b34e3001@arm.com>

On 28/06/2022 12:23, Robin Murphy wrote:
>> +
>> +    size_t
>> +    dma_opt_mapping_size(struct device *dev);
>> +
>> +Returns the maximum optimal size of a mapping for the device. Mapping 
>> large
>> +buffers may take longer so device drivers are advised to limit total DMA
>> +streaming mappings length to the returned value.
> 
> Nit: I'm not sure "advised" is necessarily the right thing to say in 
> general - that's only really true for a caller who cares about 
> throughput of churning through short-lived mappings more than anything 
> else, and doesn't take a significant hit overall from splitting up 
> larger requests. I do think it's good to clarify the exact context of 
> "optimal" here, but I'd prefer to be objectively clear that it's for 
> workloads where the up-front mapping overhead dominates.

Ok, sure, I can make that clear.

Thanks,
John

  parent reply	other threads:[~2022-06-28 11:27 UTC|newest]

Thread overview: 36+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-27 15:25 [PATCH v4 0/5] DMA mapping changes for SCSI core John Garry via iommu
2022-06-27 15:25 ` John Garry
2022-06-27 15:25 ` [PATCH v4 1/5] dma-mapping: Add dma_opt_mapping_size() John Garry via iommu
2022-06-27 15:25   ` John Garry
2022-06-28 11:23   ` Robin Murphy
2022-06-28 11:23     ` Robin Murphy
2022-06-28 11:27     ` John Garry via iommu [this message]
2022-06-28 11:27       ` John Garry
2022-06-29 11:57       ` John Garry via iommu
2022-06-29 11:57         ` John Garry
2022-06-27 15:25 ` [PATCH v4 2/5] dma-iommu: Add iommu_dma_opt_mapping_size() John Garry via iommu
2022-06-27 15:25   ` John Garry
2022-06-28 10:56   ` Robin Murphy
2022-06-28 10:56     ` Robin Murphy
2022-06-27 15:25 ` [PATCH v4 3/5] scsi: core: Cap shost max_sectors according to DMA mapping limits only once John Garry via iommu
2022-06-27 15:25   ` John Garry
2022-06-27 15:25 ` [PATCH v4 4/5] scsi: scsi_transport_sas: Cap shost max_sectors according to DMA optimal mapping limit John Garry via iommu
2022-06-27 15:25   ` John Garry
2022-06-27 15:25 ` [PATCH v4 5/5] libata-scsi: Cap ata_device->max_sectors according to shost->max_sectors John Garry via iommu
2022-06-27 15:25   ` John Garry
2022-06-27 23:24   ` Damien Le Moal via iommu
2022-06-27 23:24     ` Damien Le Moal
2022-06-28  7:54     ` John Garry via iommu
2022-06-28  7:54       ` John Garry
2022-06-28  9:14       ` Damien Le Moal via iommu
2022-06-28  9:14         ` Damien Le Moal
2022-06-28 11:33         ` John Garry via iommu
2022-06-28 11:33           ` John Garry
2022-06-29  5:40           ` Christoph Hellwig
2022-06-29  5:40             ` Christoph Hellwig
2022-06-29  5:58             ` Damien Le Moal via iommu
2022-06-29  5:58               ` Damien Le Moal
2022-06-29  7:43               ` John Garry via iommu
2022-06-29  7:43                 ` John Garry
2022-06-29  8:24                 ` Damien Le Moal via iommu
2022-06-29  8:24                   ` Damien Le Moal

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