On 08/03/2013 03:45, Nicholas A. Bellinger wrote:
+void
+iser_cq_tx_tasklet(unsigned long data)
+{
+ struct isert_conn *isert_conn = (struct isert_conn *)data;
+ struct ib_cq *tx_cq = isert_conn->conn_tx_cq;
+ struct iser_tx_desc *tx_desc;
+ struct ib_wc wc;
+
+ while (ib_poll_cq(tx_cq, 1, &wc) == 1) {
+ tx_desc = (struct iser_tx_desc *)(unsigned long)wc.wr_id;
+
+ if (wc.status == IB_WC_SUCCESS) {
+ isert_send_completion(tx_desc, isert_conn);
+ } else {
+ pr_debug("TX wc.status != IB_WC_SUCCESS >>>>>>>>>>>>>>\n");
+ isert_dump_ib_wc(&wc);
+ atomic_dec(&isert_conn->post_send_buf_count);
+ isert_cq_comp_err(tx_desc, isert_conn);
+ }
+ }
+
+ ib_req_notify_cq(tx_cq, IB_CQ_NEXT_COMP);
+}
+
+void
+isert_cq_tx_callback(struct ib_cq *cq, void *context)
+{
+ struct isert_conn *isert_conn = context;
+
+ tasklet_schedule(&isert_conn->conn_tx_tasklet);
+}
+
+void
+iser_cq_rx_tasklet(unsigned long data)
+{
+ struct isert_conn *isert_conn = (struct isert_conn *)data;
+ struct ib_cq *rx_cq = isert_conn->conn_rx_cq;
+ struct iser_rx_desc *rx_desc;
+ struct ib_wc wc;
+ unsigned long xfer_len;
+
+ while (ib_poll_cq(rx_cq, 1, &wc) == 1) {
+ rx_desc = (struct iser_rx_desc *)(unsigned long)wc.wr_id;
+
+ if (wc.status == IB_WC_SUCCESS) {
+ xfer_len = (unsigned long)wc.byte_len;
+ isert_rx_completion(rx_desc, isert_conn, xfer_len);
+ } else {
+ pr_debug("RX wc.status != IB_WC_SUCCESS >>>>>>>>>>>>>>\n");
+ if (wc.status != IB_WC_WR_FLUSH_ERR)
+ isert_dump_ib_wc(&wc);
+
+ isert_conn->post_recv_buf_count--;
+ isert_cq_comp_err(NULL, isert_conn);
+ }
+ }
+
+ ib_req_notify_cq(rx_cq, IB_CQ_NEXT_COMP);
+}
We currently have here the following sequence of calls
isert_cq_rx_callback --> tasklet_schedule ... --> ...
ib_poll_cq --> isert_rx_completion --> isert_rx_queue_desc -->
isert_rx_queue_desc --> queue_work (context switch)
isert_cq_tx_callback --> tasklet_schedule ... --> ...
ib_poll_cq --> isert_send_completion --> isert_completion_rdma_read
--> queue_work (context switch)
which means we have one context switch from the CQ callback to tasklet
and then a PER IO context switch
from the tasklet to a kernel thread context which you might need for IO
submission into the backing store.
This can be optimized by having one context switch from the isert cq
callbacks to a kernel thread, with the work
item being "do polling" and then from the cq polling code do the
submission into the backing store without
any further context switches.
Or.
+
+void
+isert_cq_rx_callback(struct ib_cq *cq, void *context)
+{
+ struct isert_conn *isert_conn = context;
+
+ tasklet_schedule(&isert_conn->conn_rx_tasklet);
+}
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