[openib-general] ib_unmap_fmr
Roland Dreier
roland at topspin.com
Wed Sep 1 18:41:44 PDT 2004
Sean> The current API for ib_unmap_fmr takes an array. A couple
Sean> of questions: Is it worth it for ib_unmap_fmr to operate on
Sean> more than a single fmr? If so, should a linked list be used
Sean> instead? And, should the access layer API assume that the
Sean> FMRs all come from the same device? My initial thought is
Sean> to restrict ib_unmap_fmr to a single fmr, _but_ if there's a
Sean> reason to unmap multiples, update struct ib_fmr to allow for
Sean> a linked list. The access layer would assume all FMRs come
Sean> from the same device in such a case, to avoid walking the
Sean> list.
One of the main reasons that FMRs (in the Mellanox Tavor sense) are a
win is that the cost of flushing the HCA's memory mapping cache can be
amortized across multiple FMRs with a single unmap call. So having
unmap_fmr operate on multiple FMRs at once is central to its
usefulness.
With that said I prefer using a linked list (and that's what I have on
my branch), and I agree with the assumption that all the FMRs come
from the same device.
- R.
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