libnvdimm: cycle flush hints

When the NFIT provides multiple flush hint addresses per-dimm it is
expressing that the platform is capable of processing multiple flush
requests in parallel.  There is some fixed cost per flush request, let
the cost be shared in parallel on multiple cpus.

Since there may not be enough flush hint addresses for each cpu to have
one, keep a per-cpu index of the last used hint, hash it with current
pid, and assume that access pattern and scheduler randomness will keep
the flush-hint usage somewhat staggered across cpus.

Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/drivers/nvdimm/nd.h b/drivers/nvdimm/nd.h
index 5912bd6b4234..40476399d227 100644
--- a/drivers/nvdimm/nd.h
+++ b/drivers/nvdimm/nd.h
@@ -52,6 +52,7 @@ struct nvdimm_drvdata {
 struct nd_region_data {
 	int ns_count;
 	int ns_active;
+	unsigned int flush_mask;
 	void __iomem *flush_wpq[0][0];
 };