From b58fc8049790ca780fb42bd2faabe9b921aedf44 Mon Sep 17 00:00:00 2001 From: Mike Marciniszyn Date: Mon, 20 Mar 2017 17:26:26 -0700 Subject: [PATCH] IB/hfi1: Eliminate synchronize_rcu() in mr delete The synchronize_rcu() call can be eliminated to improve memory deregistration performance. There are two key fields involved: - The rcu pointer itself - the lkey_published field To close the window between the rcu read of the mregion pointer and the reference count the code should: 1. To lkey/rkey validation (reader) Read the rcu pointer. If the pointer is non-NULL, get a reference. To the current validation tests use a READ_ONCE() on the lkey_published. Upon any failure release the reference. 2. To the remove logic (delete) Insure the published is zeroed prior to setting the pointer to NULL. This requires using rcu_assign_pointer() to insure lkey_published is written prior to the NULL. 3. To the insert logic (add) Insure the published is set use an rcu_assign_pointer() to insure the pointer is after all MR fields. Reviewed-by: Dennis Dalessandro Signed-off-by: Mike Marciniszyn Signed-off-by: Dennis Dalessandro Signed-off-by: Doug Ledford --- drivers/infiniband/sw/rdmavt/mr.c | 49 +++++++++++++++++++++---------- 1 file changed, 33 insertions(+), 16 deletions(-) diff --git a/drivers/infiniband/sw/rdmavt/mr.c b/drivers/infiniband/sw/rdmavt/mr.c index ae30b6838d79..7c869555cf73 100644 --- a/drivers/infiniband/sw/rdmavt/mr.c +++ b/drivers/infiniband/sw/rdmavt/mr.c @@ -191,8 +191,9 @@ static int rvt_alloc_lkey(struct rvt_mregion *mr, int dma_region) tmr = rcu_access_pointer(dev->dma_mr); if (!tmr) { - rcu_assign_pointer(dev->dma_mr, mr); mr->lkey_published = 1; + /* Insure published written first */ + rcu_assign_pointer(dev->dma_mr, mr); rvt_get_mr(mr); } goto success; @@ -224,8 +225,9 @@ static int rvt_alloc_lkey(struct rvt_mregion *mr, int dma_region) mr->lkey |= 1 << 8; rkt->gen++; } - rcu_assign_pointer(rkt->table[r], mr); mr->lkey_published = 1; + /* Insure published written first */ + rcu_assign_pointer(rkt->table[r], mr); success: spin_unlock_irqrestore(&rkt->lock, flags); out: @@ -253,23 +255,24 @@ static void rvt_free_lkey(struct rvt_mregion *mr) spin_lock_irqsave(&rkt->lock, flags); if (!lkey) { if (mr->lkey_published) { - RCU_INIT_POINTER(dev->dma_mr, NULL); + mr->lkey_published = 0; + /* insure published is written before pointer */ + rcu_assign_pointer(dev->dma_mr, NULL); rvt_put_mr(mr); } } else { if (!mr->lkey_published) goto out; r = lkey >> (32 - dev->dparms.lkey_table_size); - RCU_INIT_POINTER(rkt->table[r], NULL); + mr->lkey_published = 0; + /* insure published is written before pointer */ + rcu_assign_pointer(rkt->table[r], NULL); } - mr->lkey_published = 0; freed++; out: spin_unlock_irqrestore(&rkt->lock, flags); - if (freed) { - synchronize_rcu(); + if (freed) percpu_ref_kill(&mr->refcount); - } } static struct rvt_mr *__rvt_alloc_mr(int count, struct ib_pd *pd) @@ -822,16 +825,21 @@ int rvt_lkey_ok(struct rvt_lkey_table *rkt, struct rvt_pd *pd, goto ok; } mr = rcu_dereference(rkt->table[sge->lkey >> rkt->shift]); - if (unlikely(!mr || atomic_read(&mr->lkey_invalid) || - mr->lkey != sge->lkey || mr->pd != &pd->ibpd)) + if (!mr) goto bail; + rvt_get_mr(mr); + if (!READ_ONCE(mr->lkey_published)) + goto bail_unref; + + if (unlikely(atomic_read(&mr->lkey_invalid) || + mr->lkey != sge->lkey || mr->pd != &pd->ibpd)) + goto bail_unref; off = sge->addr - mr->user_base; if (unlikely(sge->addr < mr->user_base || off + sge->length > mr->length || (mr->access_flags & acc) != acc)) - goto bail; - rvt_get_mr(mr); + goto bail_unref; rcu_read_unlock(); off += mr->offset; @@ -867,6 +875,8 @@ int rvt_lkey_ok(struct rvt_lkey_table *rkt, struct rvt_pd *pd, isge->n = n; ok: return 1; +bail_unref: + rvt_put_mr(mr); bail: rcu_read_unlock(); return 0; @@ -922,15 +932,20 @@ int rvt_rkey_ok(struct rvt_qp *qp, struct rvt_sge *sge, } mr = rcu_dereference(rkt->table[rkey >> rkt->shift]); - if (unlikely(!mr || atomic_read(&mr->lkey_invalid) || - mr->lkey != rkey || qp->ibqp.pd != mr->pd)) + if (!mr) goto bail; + rvt_get_mr(mr); + /* insure mr read is before test */ + if (!READ_ONCE(mr->lkey_published)) + goto bail_unref; + if (unlikely(atomic_read(&mr->lkey_invalid) || + mr->lkey != rkey || qp->ibqp.pd != mr->pd)) + goto bail_unref; off = vaddr - mr->iova; if (unlikely(vaddr < mr->iova || off + len > mr->length || (mr->access_flags & acc) == 0)) - goto bail; - rvt_get_mr(mr); + goto bail_unref; rcu_read_unlock(); off += mr->offset; @@ -966,6 +981,8 @@ int rvt_rkey_ok(struct rvt_qp *qp, struct rvt_sge *sge, sge->n = n; ok: return 1; +bail_unref: + rvt_put_mr(mr); bail: rcu_read_unlock(); return 0; -- 2.20.1