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s390/pci: introduce lazy IOTLB flushing for DMA unmap

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This changes the default IOTLB flushing method to lazy flushing, which
means that there will be no direct flush after each DMA unmap operation.
Instead, the iommu bitmap pointer will be adjusted after unmap, so that
no DMA address will be re-used until after an iommu bitmap wrap-around.
The only IOTLB flush will then happen after each wrap-around.

A new kernel parameter "s390_iommu=" is also introduced, to allow changing
the flushing behaviour to the old strict method.

Reviewed-by: Sebastian Ott <[email protected]>
Signed-off-by: Gerald Schaefer <[email protected]>
Signed-off-by: Martin Schwidefsky <[email protected]>
This commit is contained in:
Gerald Schaefer 2014-07-18 17:37:08 +02:00 • committed by Martin Schwidefsky
commit c60d1ae4ef
2 changed files with 43 additions and 14 deletions
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7
Documentation/kernel-parameters.txt
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@ -3023,6 +3023,13 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
S [KNL] Run init in single mode
s390_iommu= [HW,S390]
Set s390 IOTLB flushing mode
strict
With strict flushing every unmap operation will result in
an IOTLB flush. Default is lazy flushing before reuse,
which is faster.
sa1100ir [NET]
See drivers/net/irda/sa1100_ir.c.