Re: [2.6.19 PATCH 1/7] ehea: interface to network stack

On Fri, Aug 18, 2006 at 01:29:01PM +0200, Jan-Bernd Themann wrote:

Was there noticeable performance difference when explicit prefetching is
removed? At some (invisible) point CPUs will become smarter about prefetching
than programmers and this code will be slower than possible.

+static inline struct sk_buff *get_skb_by_index(struct sk_buff **skb_array,
+					       int arr_len,
+					       struct ehea_cqe *cqe)
+{
+	struct sk_buff *skb;
+	void *pref;
+	int x;
+	int skb_index = EHEA_BMASK_GET(EHEA_WR_ID_INDEX, cqe->wr_id);
+
+	x = skb_index + 1;
+	x &= (arr_len - 1);
+
+	pref = (void*)skb_array[x];
+	prefetchw(pref);
+	prefetchw(pref + EHEA_CACHE_LINE);
+
+	pref = (void*)(skb_array[x]->data);
+	prefetch(pref);
+	prefetch(pref + EHEA_CACHE_LINE);
+	prefetch(pref + EHEA_CACHE_LINE * 2);
+	prefetch(pref + EHEA_CACHE_LINE * 3);
+	skb = skb_array[skb_index];
+	skb_array[skb_index] = NULL;
+	return skb;
+}
+
+static inline struct sk_buff *get_skb_by_index_ll(struct sk_buff **skb_array,
+						  int arr_len, int wqe_index)
+{
+	struct sk_buff *skb;
+	void *pref;
+	int x;
+
+	x = wqe_index + 1;
+	x &= (arr_len - 1);
+
+	pref = (void*)skb_array[x];
+	prefetchw(pref);
+	prefetchw(pref + EHEA_CACHE_LINE);
+
+	pref = (void*)(skb_array[x]->data);
+	prefetchw(pref);
+	prefetchw(pref + EHEA_CACHE_LINE);
+
+	skb = skb_array[wqe_index];
+	skb_array[wqe_index] = NULL;
+	return skb;
+}