Author: imp
Date: Mon Aug 28 23:54:20 2017
New Revision: 322994
URL: https://svnweb.freebsd.org/changeset/base/322994
Log:
Set the max transactions for NVMe drives better.
Provided a better estimate for the number of transactions that can be
pending at one time. This will be number of queues * number of
trackers / 4, as suggested by Jim Harris. This gives a better estimate
of the number of transactions that CAM should queue before applying
back pressure. This should be revisted when we have real multi-queue
support in CAM and the upper layers of the I/O stack.
Sponsored by: Netflix
Modified:
head/sys/dev/nvme/nvme_ctrlr.c
head/sys/dev/nvme/nvme_private.h
head/sys/dev/nvme/nvme_sim.c
Modified: head/sys/dev/nvme/nvme_ctrlr.c
==============================================================================
--- head/sys/dev/nvme/nvme_ctrlr.c Mon Aug 28 23:54:16 2017
(r322993)
+++ head/sys/dev/nvme/nvme_ctrlr.c Mon Aug 28 23:54:20 2017
(r322994)
@@ -146,6 +146,14 @@ nvme_ctrlr_construct_io_qpairs(struct nvme_controller
num_trackers = min(num_trackers, (num_entries-1));
/*
+ * Our best estimate for the maximum number of I/Os that we should
+ * noramlly have in flight at one time. This should be viewed as a hint,
+ * not a hard limit and will need to be revisitted when the upper layers
+ * of the storage system grows multi-queue support.
+ */
+ ctrlr->max_hw_pend_io = num_trackers * ctrlr->num_io_queues / 4;
+
+ /*
* This was calculated previously when setting up interrupts, but
* a controller could theoretically support fewer I/O queues than
* MSI-X vectors. So calculate again here just to be safe.
Modified: head/sys/dev/nvme/nvme_private.h
==============================================================================
--- head/sys/dev/nvme/nvme_private.h Mon Aug 28 23:54:16 2017
(r322993)
+++ head/sys/dev/nvme/nvme_private.h Mon Aug 28 23:54:20 2017
(r322994)
@@ -263,6 +263,7 @@ struct nvme_controller {
uint32_t num_io_queues;
uint32_t num_cpus_per_ioq;
+ uint32_t max_hw_pend_io;
/* Fields for tracking progress during controller initialization. */
struct intr_config_hook config_hook;
Modified: head/sys/dev/nvme/nvme_sim.c
==============================================================================
--- head/sys/dev/nvme/nvme_sim.c Mon Aug 28 23:54:16 2017
(r322993)
+++ head/sys/dev/nvme/nvme_sim.c Mon Aug 28 23:54:20 2017
(r322994)
@@ -253,7 +253,7 @@ nvme_sim_new_controller(struct nvme_controller *ctrlr)
int unit;
struct nvme_sim_softc *sc = NULL;
- max_trans = ctrlr->num_io_queues;
+ max_trans = ctrlr->max_hw_pend_io;
unit = device_get_unit(ctrlr->dev);
devq = cam_simq_alloc(max_trans);
if (devq == NULL)
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