Ubuntu Manpage: ibv_advise_mr - Gives advice or directions to the kernel about an address range belongs to a memory re‐

Provided by: libibverbs-dev_39.0-1_amd64

NAME

       ibv_advise_mr  -  Gives advice or directions to the kernel about an address range belongs to a memory re‐
       gion (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  re‐
       gion  (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.

       IBV_ADVISE_MR_ADVICE_PREFETCH_NO_FAULT
              Pre-fetch a range of an on-demand paging MR without faulting.  This allows presented pages in  the
              CPU to become presented to the device.

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_AD‐
              VISE_MR_FLAG_FLUSH : Request to be a synchronized operation.  Return to the caller after the oper‐
              ation 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. o The requested address
doesn’t belong to a MR, but a MW or something.

EPERM In one of the following: o Referencing a valid lkey outside the caller’s security scope. o The
advice is IBV_ADVISE_MR_ADVICE_PREFETCH_WRITE but the specified MR in the scatter gather list is
not registered as writable access.

ENOENT The providing lkeys aren’t consistent with the MR’s.

ENOMEM Not enough memory. # NOTES

An application may pre-fetch any address range within an ODP MR when using the IBV_ADVISE_MR_AD‐
VICE_PREFETCH or IBV_ADVISE_MR_ADVICE_PREFETCH_WRITE advice. Semantically, this operation is best-ef‐
fort. 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 trans‐
lations to the HCA. When performing a local RDMA access operation it is recommended to use IBV_AD‐
VISE_MR_FLAG_FLUSH flag with one of the pre-fetch advices to increase probability that the pages transla‐
tions are valid in the HCA and avoid future page faults.

AUTHOR