NAME

       ibv_advise_mr - Gives advice or directions to the kernel about an address range belongs to
       a memory region (MR).

SYNOPSIS

              #include <infiniband/verbs.h>

              int ibv_advise_mr(struct ibv_pd *pd,
                        enum ibv_advise_mr_advice advice,
                        uint32_t flags,
                        struct ibv_sge *sg_list,
                        uint32_t num_sge)

DESCRIPTION

       ibv_advise_mr() Give advice or directions to the kernel about an address  range  belonging
       to  a  memory  region (MR).  Applications that are aware of future access patterns can use
       this  verb  in  order  to  leverage  this  knowledge  to  improve  system  or  application
       performance.

       Conventional advice values

       IBV_ADVISE_MR_ADVICE_PREFETCH
              Pre-fetch  a  range  of  an on-demand paging MR.  Make pages present with read-only
              permission before the actual IO is conducted.  This would provide a way  to  reduce
              latency by overlapping paging-in and either compute time or IO to other ranges.

       IBV_ADVISE_MR_ADVICE_PREFETCH_WRITE
              Like IBV_ADVISE_MR_ADVICE_PREFETCH but with read-access and write-access permission
              to the fetched memory.

ARGUMENTS

       pd     The protection domain (PD) associated with the MR.

       advice The requested advise value (as listed above).

       flags  Describes the  properties  of  the  advise  operation  Conventional  advice  values
              IBV_ADVISE_MR_FLAG_FLUSH  :  Request to be a synchronized operation.  Return to the
              caller after the operation is completed.

       sg_list
              Pointer to the s/g array When using IBV_ADVISE_OP_PREFETCH advise  value,  all  the
              lkeys  of  all  the  scatter gather elements (SGEs) must be associated with ODP MRs
              (MRs that were registered with IBV_ACCESS_ON_DEMAND).

       num_sge
              Number of elements in the s/g array

RETURN VALUE

       ibv_advise_mr() returns 0 when the call was successful, or the value of errno  on  failure
       (which indicates the failure reason).

       EOPNOTSUPP
              libibverbs  or provider driver doesn’t support the ibv_advise_mr() verb (ENOSYS may
              sometimes be returned by old versions of libibverbs).

       ENOTSUP
              The advise operation isn’t supported.

       EFAULT In one of the following: o When the range requested is out of  the  MR  bounds,  or
              when  parts  of  it  are not part of the process address space.  o One of the lkeys
              provided in the scatter gather list is invalid or with wrong write access.

       EINVAL In one of the following: o The PD is invalid.  o The flags are invalid.

NOTES

       An application  may  pre-fetch  any  address  range  within  an  ODP  MR  when  using  the
       IBV_ADVISE_MR_ADVICE_PREFETCH      or      IBV_ADVISE_MR_ADVICE_PREFETCH_WRITE     advice.
       Semantically, this operation is best-effort.  That means the  kernel  does  not  guarantee
       that  underlying  pages  are  updated  in  the  HCA  or the pre-fetched pages would remain
       resident.

       When using IBV_ADVISE_MR_ADVICE_PREFETCH  or  IBV_ADVISE_MR_ADVICE_PREFETCH_WRITE  advice,
       the  operation  will  be  done in the following stages: o Page in the user pages to memory
       (pages aren’t pinned).  o Get the dma mapping of these user pages.  o Post the  underlying
       page translations to the HCA.

       If  IBV_ADVISE_MR_FLAG_FLUSH  is  specified then the underlying pages are guaranteed to be
       updated in the HCA before returning SUCCESS.  Otherwise the driver can choose to  postpone
       the  posting  of  the  new  translations  to the HCA.  When performing a local RDMA access
       operation it is recommended to use IBV_ADVISE_MR_FLAG_FLUSH flag with one of the pre-fetch
       advices to increase probability that the pages translations are valid in the HCA and avoid
       future page faults.

SEE ALSO

       ibv_reg_mr(3), ibv_rereg_mr(3), ibv_dereg_mr(3)

AUTHOR

       Aviad Yehezkel <aviadye@mellanox.com>