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scsi: scsi_transport_sas: cap shost opt_sectors according to DMA optimal limit

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Streaming DMA mappings may be considerably slower when mappings go through
an IOMMU and the total mapping length is somewhat long. This is because the
IOMMU IOVA code allocates and free an IOVA for each mapping, which may
affect performance.

For performance reasons set the request queue max_sectors from
dma_opt_mapping_size(), which knows this mapping limit.

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
This commit is contained in:
John Garry 2022-07-14 19:15:28 +08:00 committed by Christoph Hellwig
parent 608128d391
commit 4cbfca5f77
1 changed files with 6 additions and 0 deletions
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6
drivers/scsi/scsi_transport_sas.c
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@ -225,6 +225,7 @@ static int sas_host_setup(struct transport_container *tc, struct device *dev,
{
struct Scsi_Host *shost = dev_to_shost(dev);
struct sas_host_attrs *sas_host = to_sas_host_attrs(shost);
struct device *dma_dev = shost->dma_dev;
INIT_LIST_HEAD(&sas_host->rphy_list);
mutex_init(&sas_host->lock);
@ -236,6 +237,11 @@ static int sas_host_setup(struct transport_container *tc, struct device *dev,
dev_printk(KERN_ERR, dev, "fail to a bsg device %d\n",
shost->host_no);
if (dma_dev->dma_mask) {
shost->opt_sectors = min_t(unsigned int, shost->max_sectors,
dma_opt_mapping_size(dma_dev) >> SECTOR_SHIFT);
}
return 0;
}