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Date:      Mon, 4 Dec 2017 21:50:27 +0000 (UTC)
From:      Rick Macklem <rmacklem@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r326544 - head/sys/fs/nfsserver
Message-ID:  <201712042150.vB4LoR1c018653@repo.freebsd.org>
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Author: rmacklem
Date: Mon Dec  4 21:50:27 2017
New Revision: 326544
URL: https://svnweb.freebsd.org/changeset/base/326544

Log:
  Avoid the overhead of acquiring a lock in nfsrv_checkgetattr() when
  there are no write delegations issued.
  
  manu@ reported on the freebsd-current@ mailing list that there was
  a significant performance hit in nfsrv_checkgetattr() caused by
  the acquisition/release of a state lock, even when there were no
  write delegations issued.
  This patch add a count of outstanding issued write delegations to the
  NFSv4 server. This count allows nfsrv_checkgetattr() to return without
  acquiring any lock when the count is 0, avoiding the performance hit
  for the case where no write delegations are issued.
  
  Reported by:	manu
  Reviewed by:	kib
  MFC after:	2 weeks
  Differential Revision:	https://reviews.freebsd.org/D13327

Modified:
  head/sys/fs/nfsserver/nfs_nfsdstate.c

Modified: head/sys/fs/nfsserver/nfs_nfsdstate.c
==============================================================================
--- head/sys/fs/nfsserver/nfs_nfsdstate.c	Mon Dec  4 21:12:05 2017	(r326543)
+++ head/sys/fs/nfsserver/nfs_nfsdstate.c	Mon Dec  4 21:50:27 2017	(r326544)
@@ -95,6 +95,7 @@ static time_t nfsrvboottime;
 static int nfsrv_returnoldstateid = 0, nfsrv_clients = 0;
 static int nfsrv_clienthighwater = NFSRV_CLIENTHIGHWATER;
 static int nfsrv_nogsscallback = 0;
+static volatile int nfsrv_writedelegcnt = 0;
 
 /* local functions */
 static void nfsrv_dumpaclient(struct nfsclient *clp,
@@ -1263,6 +1264,8 @@ nfsrv_freedeleg(struct nfsstate *stp)
 	LIST_REMOVE(stp, ls_hash);
 	LIST_REMOVE(stp, ls_list);
 	LIST_REMOVE(stp, ls_file);
+	if ((stp->ls_flags & NFSLCK_DELEGWRITE) != 0)
+		nfsrv_writedelegcnt--;
 	lfp = stp->ls_lfp;
 	if (LIST_EMPTY(&lfp->lf_open) &&
 	    LIST_EMPTY(&lfp->lf_lock) && LIST_EMPTY(&lfp->lf_deleg) &&
@@ -2907,6 +2910,7 @@ tryagain:
 		    new_deleg->ls_flags = (NFSLCK_DELEGWRITE |
 			NFSLCK_READACCESS | NFSLCK_WRITEACCESS);
 		    *rflagsp |= NFSV4OPEN_WRITEDELEGATE;
+		    nfsrv_writedelegcnt++;
 		} else {
 		    new_deleg->ls_flags = (NFSLCK_DELEGREAD |
 			NFSLCK_READACCESS);
@@ -3037,6 +3041,7 @@ tryagain:
 			new_deleg->ls_clp = clp;
 			new_deleg->ls_filerev = filerev;
 			new_deleg->ls_compref = nd->nd_compref;
+			nfsrv_writedelegcnt++;
 			LIST_INSERT_HEAD(&lfp->lf_deleg, new_deleg, ls_file);
 			LIST_INSERT_HEAD(NFSSTATEHASH(clp,
 			    new_deleg->ls_stateid), new_deleg, ls_hash);
@@ -3094,6 +3099,7 @@ tryagain:
 			    new_deleg->ls_flags = (NFSLCK_DELEGWRITE |
 				NFSLCK_READACCESS | NFSLCK_WRITEACCESS);
 			    *rflagsp |= NFSV4OPEN_WRITEDELEGATE;
+			    nfsrv_writedelegcnt++;
 			} else {
 			    new_deleg->ls_flags = (NFSLCK_DELEGREAD |
 				NFSLCK_READACCESS);
@@ -3170,6 +3176,7 @@ tryagain:
 					     NFSLCK_READACCESS |
 					     NFSLCK_WRITEACCESS);
 					*rflagsp |= NFSV4OPEN_WRITEDELEGATE;
+					nfsrv_writedelegcnt++;
 				} else {
 					new_deleg->ls_flags =
 					    (NFSLCK_DELEGREAD |
@@ -5299,6 +5306,8 @@ nfsrv_checkgetattr(struct nfsrv_descript *nd, vnode_t 
 
 	NFSCBGETATTR_ATTRBIT(attrbitp, &cbbits);
 	if (!NFSNONZERO_ATTRBIT(&cbbits))
+		goto out;
+	if (nfsrv_writedelegcnt == 0)
 		goto out;
 
 	/*

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