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Subject[PATCH] scsi: hisi_sas: Limit max hw sectors for v3 HW
Date
If the controller is behind an IOMMU then the IOMMU IOVA caching range can
affect performance, as discussed in [0].

Limit the max HW sectors to not exceed this limit. We need to hardcode
the value until a proper DMA mapping API is available.

[0] https://lore.kernel.org/linux-iommu/20210129092120.1482-1-thunder.leizhen@huawei.com/

Signed-off-by: John Garry <john.garry@huawei.com>
---
This patch is intended as something which I can backport to stable.
Series [1] is a proper fix but stuck, but I would not plan to backport
it anyway.
[1] https://lore.kernel.org/linux-scsi/1654507822-168026-1-git-send-email-john.garry@huawei.com/T/#m069f33edd547533301e2af156ebd6badee199dea

diff --git a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
index 7d819fc0395e..eb86afb21aab 100644
--- a/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
+++ b/drivers/scsi/hisi_sas/hisi_sas_v3_hw.c
@@ -2782,6 +2782,7 @@ static int slave_configure_v3_hw(struct scsi_device *sdev)
struct hisi_hba *hisi_hba = shost_priv(shost);
struct device *dev = hisi_hba->dev;
int ret = sas_slave_configure(sdev);
+ unsigned int max_sectors;

if (ret)
return ret;
@@ -2799,6 +2800,12 @@ static int slave_configure_v3_hw(struct scsi_device *sdev)
}
}

+ /* Set according to IOMMU IOVA caching limit */
+ max_sectors = min_t(size_t, queue_max_hw_sectors(sdev->request_queue),
+ (PAGE_SIZE * 32) >> SECTOR_SHIFT);
+
+ blk_queue_max_hw_sectors(sdev->request_queue, max_sectors);
+
return 0;
}

--
2.35.3
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