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 <uchen@cn.ibm.com>
Signed-off-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
diff --git a/drivers/misc/cxl/context.c b/drivers/misc/cxl/context.c
index d1b55fe..78ce990 100644
--- a/drivers/misc/cxl/context.c
+++ b/drivers/misc/cxl/context.c
@@ -232,12 +232,9 @@
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 @@
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);
+}
