On 6/30/22 21:08, John Garry wrote: > 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 <[email protected]> > --- > drivers/scsi/scsi_transport_sas.c | 6 ++++++ > 1 file changed, 6 insertions(+) > > diff --git a/drivers/scsi/scsi_transport_sas.c > b/drivers/scsi/scsi_transport_sas.c > index 12bff64dade6..1b45248748e0 100644 > --- a/drivers/scsi/scsi_transport_sas.c > +++ b/drivers/scsi/scsi_transport_sas.c > @@ -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) { > + shost->max_sectors = min_t(unsigned int, shost->max_sectors, > + dma_opt_mapping_size(dma_dev) >> SECTOR_SHIFT); > + }
Hmm... shost->max_sectors becomes the max_hw_sectors limit for the block dev. So using dma_max_mapping_size(dma_dev) for that limit makes sense. Shouldn't dma_opt_mapping_size(dma_dev) be used to limit only the default "soft" limit (queue max_sectors limit) instead of the hard limit ? > + > return 0; > } > -- Damien Le Moal Western Digital Research _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
