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Date: Sat, 21 May 2022 08:30:30 +0900 From: Damien Le Moal <damien.lemoal@...nsource.wdc.com> To: John Garry <john.garry@...wei.com>, joro@...tes.org, will@...nel.org, jejb@...ux.ibm.com, martin.petersen@...cle.com, hch@....de, m.szyprowski@...sung.com, robin.murphy@....com Cc: linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-ide@...r.kernel.org, iommu@...ts.linux-foundation.org, linux-scsi@...r.kernel.org, liyihang6@...ilicon.com, chenxiang66@...ilicon.com, thunder.leizhen@...wei.com Subject: Re: [PATCH 3/4] scsi: core: Cap shost max_sectors according to DMA optimum mapping limits On 5/20/22 17:23, 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. > > In addition, the shost->max_sectors is repeatedly set for each sdev in > __scsi_init_queue(). This is unnecessary, so set once when adding the > host. > > Signed-off-by: John Garry <john.garry@...wei.com> > --- > drivers/scsi/hosts.c | 5 +++++ > drivers/scsi/scsi_lib.c | 4 ---- > 2 files changed, 5 insertions(+), 4 deletions(-) > > diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c > index f69b77cbf538..a3ae6345473b 100644 > --- a/drivers/scsi/hosts.c > +++ b/drivers/scsi/hosts.c > @@ -225,6 +225,11 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev, > shost->cmd_per_lun = min_t(int, shost->cmd_per_lun, > shost->can_queue); > > + if (dma_dev->dma_mask) { > + shost->max_sectors = min_t(unsigned int, shost->max_sectors, > + dma_opt_mapping_size(dma_dev) >> SECTOR_SHIFT); > + } Nit: you could drop the curly brackets here. > + > error = scsi_init_sense_cache(shost); > if (error) > goto fail; > diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c > index 8d18cc7e510e..2d43bb8799bd 100644 > --- a/drivers/scsi/scsi_lib.c > +++ b/drivers/scsi/scsi_lib.c > @@ -1884,10 +1884,6 @@ void __scsi_init_queue(struct Scsi_Host *shost, struct request_queue *q) > blk_queue_max_integrity_segments(q, shost->sg_prot_tablesize); > } > > - if (dev->dma_mask) { > - shost->max_sectors = min_t(unsigned int, shost->max_sectors, > - dma_max_mapping_size(dev) >> SECTOR_SHIFT); > - } > blk_queue_max_hw_sectors(q, shost->max_sectors); > blk_queue_segment_boundary(q, shost->dma_boundary); > dma_set_seg_boundary(dev, shost->dma_boundary); Reviewed-by: Damien Le Moal <damien.lemoal@...nsource.wdc.com> -- Damien Le Moal Western Digital Research
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