From 8ac75b96be71e20ec1785ca18170890c4dfffe87 Mon Sep 17 00:00:00 2001 From: Ian Munsie Date: Fri, 8 May 2015 22:55:18 +1000 Subject: [PATCH] cxl: Use call_rcu to reduce latency when releasing the afu fd The afu fd release path was identified as a significant bottleneck in the overall performance of cxl. While an optimal AFU design would minimise the need to close & reopen the AFU fd, it is not always practical to avoid. The bottleneck seems to be down to the call to synchronize_rcu(), which will block until every other thread is guaranteed to be out of an RCU critical section. Replace it with call_rcu() to free the context structures later so we can return to the application sooner. This reduces the time spent in the fd release path from 13356 usec to 13.3 usec - about a 100x speed up. Reported-by: Fei K Chen Signed-off-by: Ian Munsie Signed-off-by: Michael Ellerman --- drivers/misc/cxl/context.c | 15 ++++++++++----- drivers/misc/cxl/cxl.h | 2 ++ 2 files changed, 12 insertions(+), 5 deletions(-) diff --git a/drivers/misc/cxl/context.c b/drivers/misc/cxl/context.c index d1b55fe62817..78ce990d77ca 100644 --- a/drivers/misc/cxl/context.c +++ b/drivers/misc/cxl/context.c @@ -232,12 +232,9 @@ void cxl_context_detach_all(struct cxl_afu *afu) mutex_unlock(&afu->contexts_lock); } -void cxl_context_free(struct cxl_context *ctx) +static void reclaim_ctx(struct rcu_head *rcu) { - mutex_lock(&ctx->afu->contexts_lock); - idr_remove(&ctx->afu->contexts_idr, ctx->pe); - mutex_unlock(&ctx->afu->contexts_lock); - synchronize_rcu(); + struct cxl_context *ctx = container_of(rcu, struct cxl_context, rcu); free_page((u64)ctx->sstp); ctx->sstp = NULL; @@ -245,3 +242,11 @@ void cxl_context_free(struct cxl_context *ctx) put_pid(ctx->pid); kfree(ctx); } + +void cxl_context_free(struct cxl_context *ctx) +{ + mutex_lock(&ctx->afu->contexts_lock); + idr_remove(&ctx->afu->contexts_idr, ctx->pe); + mutex_unlock(&ctx->afu->contexts_lock); + call_rcu(&ctx->rcu, reclaim_ctx); +} diff --git a/drivers/misc/cxl/cxl.h b/drivers/misc/cxl/cxl.h index cfee819bf5d4..b361b48d1b01 100644 --- a/drivers/misc/cxl/cxl.h +++ b/drivers/misc/cxl/cxl.h @@ -457,6 +457,8 @@ struct cxl_context { bool pending_irq; bool pending_fault; bool pending_afu_err; + + struct rcu_head rcu; }; struct cxl { -- 2.20.1