Profiling has shown the the atomic is a performance issue
for the pio hot path.
If multiple cpus allocated an sc's buffer, the cacheline
containing the atomic will bounce from L0 to L0.
Convert the atomic to a percpu variable.
Reviewed-by: Jubin John <jubin.john@xxxxxxxxx>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@xxxxxxxxx>
---
drivers/staging/rdma/hfi1/pio.c | 40 ++++++++++++++++++++++++++++++----
drivers/staging/rdma/hfi1/pio.h | 2 +-
drivers/staging/rdma/hfi1/pio_copy.c | 6 +++--
3 files changed, 40 insertions(+), 8 deletions(-)
diff --git a/drivers/staging/rdma/hfi1/pio.c b/drivers/staging/rdma/hfi1/pio.c
index eab58c1..ed8043b 100644
--- a/drivers/staging/rdma/hfi1/pio.c
+++ b/drivers/staging/rdma/hfi1/pio.c
@@ -660,6 +660,24 @@ void set_pio_integrity(struct send_context *sc)
write_kctxt_csr(dd, hw_context, SC(CHECK_ENABLE), reg);
}
+static u32 get_buffers_allocated(struct send_context *sc)
+{
+ int cpu;
+ u32 ret = 0;
+
+ for_each_possible_cpu(cpu)
+ ret += *per_cpu_ptr(sc->buffers_allocated, cpu);
+ return ret;
+}
+
+static void reset_buffers_allocated(struct send_context *sc)
+{
+ int cpu;
+
+ for_each_possible_cpu(cpu)
+ (*per_cpu_ptr(sc->buffers_allocated, cpu)) = 0;
+}
+
/*
* Allocate a NUMA relative send context structure of the given type along
* with a HW context.
@@ -668,7 +686,7 @@ struct send_context *sc_alloc(struct hfi1_devdata *dd, int type,
uint hdrqentsize, int numa)
{
struct send_context_info *sci;
- struct send_context *sc;
+ struct send_context *sc = NULL;
dma_addr_t pa;
unsigned long flags;
u64 reg;
@@ -686,10 +704,20 @@ struct send_context *sc_alloc(struct hfi1_devdata *dd, int type,
if (!sc)
return NULL;
+ sc->buffers_allocated = alloc_percpu(u32);
+ if (!sc->buffers_allocated) {
+ kfree(sc);
+ dd_dev_err(dd,
+ "Cannot allocate buffers_allocated per cpu counters\n"
+ );
+ return NULL;
+ }
+
spin_lock_irqsave(&dd->sc_lock, flags);
ret = sc_hw_alloc(dd, type, &sw_index, &hw_context);
if (ret) {
spin_unlock_irqrestore(&dd->sc_lock, flags);
+ free_percpu(sc->buffers_allocated);
kfree(sc);
return NULL;
}
@@ -705,7 +733,6 @@ struct send_context *sc_alloc(struct hfi1_devdata *dd, int type,
spin_lock_init(&sc->credit_ctrl_lock);
INIT_LIST_HEAD(&sc->piowait);
INIT_WORK(&sc->halt_work, sc_halted);
- atomic_set(&sc->buffers_allocated, 0);
init_waitqueue_head(&sc->halt_wait);
/* grouping is always single context for now */
@@ -866,6 +893,7 @@ void sc_free(struct send_context *sc)
spin_unlock_irqrestore(&dd->sc_lock, flags);
kfree(sc->sr);
+ free_percpu(sc->buffers_allocated);
kfree(sc);
}
@@ -1029,7 +1057,7 @@ int sc_restart(struct send_context *sc)
/* kernel context */
loop = 0;
while (1) {
- count = atomic_read(&sc->buffers_allocated);
+ count = get_buffers_allocated(sc);
if (count == 0)
break;
if (loop > 100) {
@@ -1197,7 +1225,8 @@ int sc_enable(struct send_context *sc)
sc->sr_head = 0;
sc->sr_tail = 0;
sc->flags = 0;
- atomic_set(&sc->buffers_allocated, 0);
+ /* the alloc lock insures no fast path allocation */
+ reset_buffers_allocated(sc);
/*
* Clear all per-context errors. Some of these will be set when
@@ -1373,7 +1402,8 @@ retry:
/* there is enough room */
- atomic_inc(&sc->buffers_allocated);
+ preempt_disable();
+ this_cpu_inc(*sc->buffers_allocated);
/* read this once */
head = sc->sr_head;
diff --git a/drivers/staging/rdma/hfi1/pio.h b/drivers/staging/rdma/hfi1/pio.h
index 0bb885c..53d3e0a 100644
--- a/drivers/staging/rdma/hfi1/pio.h
+++ b/drivers/staging/rdma/hfi1/pio.h
@@ -130,7 +130,7 @@ struct send_context {
spinlock_t credit_ctrl_lock ____cacheline_aligned_in_smp;
u64 credit_ctrl; /* cache for credit control */
u32 credit_intr_count; /* count of credit intr users */
- atomic_t buffers_allocated; /* count of buffers allocated */
+ u32 __percpu *buffers_allocated;/* count of buffers allocated */
wait_queue_head_t halt_wait; /* wait until kernel sees interrupt */
};
diff --git a/drivers/staging/rdma/hfi1/pio_copy.c b/drivers/staging/rdma/hfi1/pio_copy.c
index 8972bbc..ebb0baf 100644
--- a/drivers/staging/rdma/hfi1/pio_copy.c
+++ b/drivers/staging/rdma/hfi1/pio_copy.c
@@ -160,7 +160,8 @@ void pio_copy(struct hfi1_devdata *dd, struct pio_buf *pbuf, u64 pbc,
}
/* finished with this buffer */
- atomic_dec(&pbuf->sc->buffers_allocated);
+ this_cpu_dec(*pbuf->sc->buffers_allocated);
+ preempt_enable();
}
/* USE_SHIFTS is faster in user-space tests on a Xeon X5570 @ 2.93GHz */
@@ -854,5 +855,6 @@ void seg_pio_copy_end(struct pio_buf *pbuf)
}
/* finished with this buffer */
- atomic_dec(&pbuf->sc->buffers_allocated);
+ this_cpu_dec(*pbuf->sc->buffers_allocated);
+ preempt_enable();
}
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