svn commit: r361808 - stable/12/sys/netinet/cc

[Richard Scheffenegger]

Author: rscheff
Date: Thu Jun  4 21:02:24 2020
New Revision: 361808
URL: https://svnweb.freebsd.org/changeset/base/361808

Log:
  MFC rS361348: DCTCP: update alpha only once after loss recovery.
  
  In mixed ECN marking and loss scenarios it was found, that
  the alpha value of DCTCP is updated two times. The second
  update happens with freshly initialized counters indicating
  to ECN loss. Overall this leads to alpha not adjusting as
  quickly as expected to ECN markings, and therefore lead to
  excessive loss.
  
  Reported by:	Cheng Cui
  Reviewed by:	chengc_netapp.com, rrs, tuexen (mentor)
  Approved by:	tuexen (mentor), rgrimes (mentor, blanket)
  Sponsored by:	NetApp, Inc.
  Differential Revision:	https://reviews.freebsd.org/D24817

Modified:
  stable/12/sys/netinet/cc/cc_dctcp.c
Directory Properties:
  stable/12/   (props changed)

Modified: stable/12/sys/netinet/cc/cc_dctcp.c
==============================================================================
--- stable/12/sys/netinet/cc/cc_dctcp.c	Thu Jun  4 20:48:57 2020	(r361807)
+++ stable/12/sys/netinet/cc/cc_dctcp.c	Thu Jun  4 21:02:24 2020	(r361808)
@@ -154,10 +154,8 @@ dctcp_ack_received(struct cc_var *ccv, uint16_t type)
 		 * Update the fraction of marked bytes at the end of
 		 * current window size.
 		 */
-		if ((IN_FASTRECOVERY(CCV(ccv, t_flags)) &&
-		    SEQ_GEQ(ccv->curack, CCV(ccv, snd_recover))) ||
-		    (!IN_FASTRECOVERY(CCV(ccv, t_flags)) &&
-		    SEQ_GT(ccv->curack, dctcp_data->save_sndnxt)))
+		if (!IN_FASTRECOVERY(CCV(ccv, t_flags)) &&
+		    SEQ_GT(ccv->curack, dctcp_data->save_sndnxt))
 			dctcp_update_alpha(ccv);
 	} else
 		newreno_cc_algo.ack_received(ccv, type);