qcacld: TxRx: Reduce CPU cycles for ol_tx_desc_ll() in Tx path.

HTT/HTC Tx descriptor resides in un-cached memory.
Current implementation of htt_tx_desc_init() causes memory
to be accessed for every bit being set in the 0th & 1st
words of the HTT/HTC descriptor. The current fix uses local
variables (& hence cached writes) to initialize the bits of
word0 & word1, before finally commiting this to memory.
Use of cached writes reduces the overall CPU utilization of the
calling function ol_tx_desc_ll() (as shown by "perf") by 2 to
5%. This fix is required to reduce the overall latency in the Tx path.

Change-Id: Icfaa8f83b93eb890ef688302d2f6269daad72f1a

1 files changed, 18 insertions, 11 deletions

diff --git a/CORE/SERVICES/COMMON/ol_htt_tx_api.h b/CORE/SERVICES/COMMON/ol_htt_tx_api.h
index 916a010db672..03d816831094 100644
--- a/CORE/SERVICES/COMMON/ol_htt_tx_api.h
+++ b/CORE/SERVICES/COMMON/ol_htt_tx_api.h
@@ -385,10 +385,10 @@ htt_tx_desc_init(
     struct htt_msdu_info_t *msdu_info)
 {
     u_int32_t *word0, *word1, *word3;
+    u_int32_t local_word0, local_word1;
     struct htt_host_tx_desc_t *htt_host_tx_desc = (struct htt_host_tx_desc_t *)
         (((char *) htt_tx_desc) - HTT_TX_DESC_VADDR_OFFSET);
 
-
     word0 = (u_int32_t *) htt_tx_desc;
     word1 = word0 + 1;
     /*
@@ -397,18 +397,25 @@ htt_tx_desc_init(
      */
     word3 = word0 + 3; // Dword 3
 
-    *word0 = 0;
+    /*
+     * HTT Tx Desc is in uncached memory. Used cached writes per word, to
+     * reduce unnecessary memory access.
+     */
+
+    local_word0 = 0;
+    HTT_H2T_MSG_TYPE_SET(local_word0, HTT_H2T_MSG_TYPE_TX_FRM);
+    HTT_TX_DESC_PKT_TYPE_SET(local_word0, msdu_info->info.l2_hdr_type);
+    HTT_TX_DESC_VDEV_ID_SET(local_word0, msdu_info->info.vdev_id);
+    HTT_TX_DESC_EXT_TID_SET(local_word0, msdu_info->info.ext_tid);
+    HTT_TX_DESC_CKSUM_OFFLOAD_SET(local_word0, msdu_info->action.cksum_offload);
+    HTT_TX_DESC_NO_ENCRYPT_SET(local_word0, msdu_info->action.do_encrypt ? 0 : 1);
+    *word0 = local_word0;
 
-    HTT_H2T_MSG_TYPE_SET(*word0, HTT_H2T_MSG_TYPE_TX_FRM);
-    HTT_TX_DESC_PKT_TYPE_SET(*word0, msdu_info->info.l2_hdr_type);
-    HTT_TX_DESC_VDEV_ID_SET(*word0, msdu_info->info.vdev_id);
-    HTT_TX_DESC_EXT_TID_SET(*word0, msdu_info->info.ext_tid);
-    HTT_TX_DESC_CKSUM_OFFLOAD_SET(*word0, msdu_info->action.cksum_offload);
-    HTT_TX_DESC_NO_ENCRYPT_SET(*word0, msdu_info->action.do_encrypt ? 0 : 1);
+    local_word1 = 0;
+    HTT_TX_DESC_FRM_LEN_SET(local_word1, adf_nbuf_len(msdu));
+    HTT_TX_DESC_FRM_ID_SET(local_word1, msdu_id);
+    *word1 = local_word1;
 
-    *word1 = 0;
-    HTT_TX_DESC_FRM_LEN_SET(*word1, adf_nbuf_len(msdu));
-    HTT_TX_DESC_FRM_ID_SET(*word1, msdu_id);
     /* Initialize peer_id to INVALID_PEER bcoz this is NOT Reinjection path*/
     *word3 = HTT_INVALID_PEER;