Re: [dpdk-dev] [PATCH 07/21] vhost: add iotlb helper functions

[Yuanhan Liu <yliu@fridaylinux.org>]

On Fri, Sep 08, 2017 at 10:24:58AM +0200, Maxime Coquelin wrote:
> 
> 
> On 09/08/2017 10:08 AM, Yuanhan Liu wrote:
> >On Thu, Aug 31, 2017 at 11:50:09AM +0200, Maxime Coquelin wrote:
> >>diff --git a/lib/librte_vhost/iotlb.c b/lib/librte_vhost/iotlb.c
> >>new file mode 100644
> >>index 000000000..1b739dae5
> >>--- /dev/null
> >>+++ b/lib/librte_vhost/iotlb.c
> >>@@ -0,0 +1,231 @@
> >>+/*-
> >>+ *   BSD LICENSE
> >>+ *
> >>+ *   Copyright (c) 2017 Red Hat, Inc.
> >>+ *   Copyright (c) 2017 Maxime Coquelin <maxime.coquelin@redhat.com>
> >
> >I'm not a lawer, but I have been told many years before, that you don't
> >have the copyright for the code you write for open source project, the
> >company you work for does.
> >
> >Thus, it's more common to see something like following:
> >	Copyright , ... the commany ...
> >	Author:  Some One <...@...>
> >
> >However, as you may have noticed, it's not common to put the authorship
> >in the source files. Though I don't object it.
> 
> I'm not a lawyer too. At least in other projects, it seems common the
> author puts his name as copyright owner.
> 
> I have no issue to change it to only keep Red Hat's one though.

That's up to you. What I said before was JFYI :)

> >[...]
> >>+#define IOTLB_CACHE_SIZE 1024
> >>+
> >>+static void vhost_user_iotlb_cache_remove_all(struct vhost_virtqueue *vq)
> >    ^^^^^^^^^^^^
> >Note that it's not the DPDK coding style to define a function.
> 
> Ok, I guess you mean:
> static void
> vhost_user_iotlb_cache_remove_all(struct vhost_virtqueue *vq) ?

Yep.

> >>+{
> >>+	struct vhost_iotlb_entry *node, *temp_node;
> >>+
> >>+	rte_rwlock_write_lock(&vq->iotlb_lock);
> >>+
> >>+	TAILQ_FOREACH_SAFE(node, &vq->iotlb_list, next, temp_node) {
> >>+		TAILQ_REMOVE(&vq->iotlb_list, node, next);
> >>+		rte_mempool_put(vq->iotlb_pool, node);
> >>+	}
> >>+
> >>+	rte_rwlock_write_unlock(&vq->iotlb_lock);
> >>+}
> >>+
> >>+void vhost_user_iotlb_cache_insert(struct vhost_virtqueue *vq, uint64_t iova,
> >>+				uint64_t uaddr, uint64_t size, uint8_t perm)
> >>+{
> >>+	struct vhost_iotlb_entry *node, *new_node;
> >>+	int ret;
> >>+
> >>+	ret = rte_mempool_get(vq->iotlb_pool, (void **)&new_node);
> >>+	if (ret) {
> >>+		RTE_LOG(ERR, VHOST_CONFIG, "IOTLB pool empty, invalidate cache\n");
> >
> >It's a cache, why not considering remove one to get space for new one?
> 
> It would mean having to track every lookups not to remove hot entries,
> which would have an impact on performance.

You were removing all caches, how can we do worse than that? Even a
random evict would be better. Or, more simply, just to remove the
head or the tail?

	--yliu

> Moreover, the idea is to have the cache large enough, else you could
> face packet drops due to random cache misses.
> 
> We might consider to improve it, but I consider it an optimization that
> could be implemented later if needed.
> 
> >>+		vhost_user_iotlb_cache_remove_all(vq);
> >>+		ret = rte_mempool_get(vq->iotlb_pool, (void **)&new_node);
> >>+		if (ret) {
> >>+			RTE_LOG(ERR, VHOST_CONFIG, "IOTLB pool still empty, failure\n");
> >>+			return;
> >>+		}
> >>+	}