From: John Garry <john.garry@huawei.com>
To: "Martin K. Petersen" <martin.petersen@oracle.com>,
Christoph Hellwig <hch@lst.de>
Cc: <damien.lemoal@opensource.wdc.com>, <joro@8bytes.org>,
<will@kernel.org>, <jejb@linux.ibm.com>,
<m.szyprowski@samsung.com>, <robin.murphy@arm.com>,
<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 v5 0/5] DMA mapping changes for SCSI core
Date: Fri, 8 Jul 2022 17:17:06 +0100 [thread overview]
Message-ID: <5fd4814a-81b1-0e71-58e0-57a747eb684e@huawei.com> (raw)
In-Reply-To: <yq1y1x47jgn.fsf@ca-mkp.ca.oracle.com>
On 07/07/2022 21:35, Martin K. Petersen wrote:
> Christoph,
>
>> Yes, I've mostly been waiting for an ACK from Martin.
> Sorry, I'm on vacation this week. The series looks OK to me although I
> do agree that it would be great if the max was reflected in the queue's
> hard limit and opt in the soft limit.
Ah, I think that I misunderstood Damien's question. I thought he was
asking why not keep shost max_sectors at dma_max_mapping_size() and then
init each sdev request queue max hw sectors at dma_opt_mapping_size().
But he seems that you want to know why not have the request queue max
sectors at dma_opt_mapping_size(). The answer is related to meaning of
dma_opt_mapping_size(). If we get any mappings which exceed this size
then it can have a big dma mapping performance hit. So I set max hw
sectors at this ‘opt’ mapping size to ensure that we get no mappings
which exceed this size. Indeed, I think max sectors is 128Kb today for
my host, which would be same as dma_opt_mapping_size() value with an
IOMMU enabled. And I find that only a small % of request size may exceed
this 128kb size, but it still has a big performance impact.
>
> Acked-by: Martin K. Petersen<martin.petersen@oracle.com>
Thanks,
John
next prev parent reply other threads:[~2022-07-08 16:17 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-30 12:08 [PATCH v5 0/5] DMA mapping changes for SCSI core John Garry
2022-06-30 12:08 ` [PATCH v5 1/5] dma-mapping: Add dma_opt_mapping_size() John Garry
2022-06-30 12:08 ` [PATCH v5 2/5] dma-iommu: Add iommu_dma_opt_mapping_size() John Garry
2022-06-30 12:08 ` [PATCH v5 3/5] scsi: core: Cap shost max_sectors according to DMA limits only once John Garry
2022-06-30 23:41 ` Damien Le Moal
2022-07-01 8:02 ` John Garry
2022-06-30 12:08 ` [PATCH v5 4/5] scsi: scsi_transport_sas: Cap shost max_sectors according to DMA optimal limit John Garry
2022-06-30 23:49 ` Damien Le Moal
2022-07-01 8:46 ` John Garry
2022-06-30 12:08 ` [PATCH v5 5/5] ata: libata-scsi: Cap ata_device->max_sectors according to shost->max_sectors John Garry
2022-07-06 13:40 ` [PATCH v5 0/5] DMA mapping changes for SCSI core John Garry
2022-07-06 13:44 ` Christoph Hellwig
2022-07-07 20:35 ` Martin K. Petersen
2022-07-08 16:17 ` John Garry [this message]
2022-07-10 23:08 ` Damien Le Moal
2022-07-11 7:36 ` John Garry
2022-07-11 10:40 ` Damien Le Moal
2022-07-11 14:49 ` John Garry
2022-07-14 3:10 ` Martin K. Petersen
2022-07-14 7:52 ` John Garry
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