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Date:      Thu, 14 Jun 2018 11:09:52 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r335132 - in head/sys: amd64/amd64 i386/i386
Message-ID:  <201806141109.w5EB9qGk002680@repo.freebsd.org>
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Author: kib
Date: Thu Jun 14 11:09:51 2018
New Revision: 335132
URL: https://svnweb.freebsd.org/changeset/base/335132

Log:
  Reorganize code flow in fpudna()/npxdna() to highlight the critical
  section scope.  Sprinkle __predict_false() for conditions known to
  never occur or occur only on rare platforms.
  
  Sponsored by:	The FreeBSD Foundation

Modified:
  head/sys/amd64/amd64/fpu.c
  head/sys/i386/i386/npx.c

Modified: head/sys/amd64/amd64/fpu.c
==============================================================================
--- head/sys/amd64/amd64/fpu.c	Thu Jun 14 10:33:26 2018	(r335131)
+++ head/sys/amd64/amd64/fpu.c	Thu Jun 14 11:09:51 2018	(r335132)
@@ -722,7 +722,7 @@ fpudna(void)
 
 	KASSERT((curpcb->pcb_flags & PCB_FPUNOSAVE) == 0,
 	    ("fpudna while in fpu_kern_enter(FPU_KERN_NOCTX)"));
-	if (PCPU_GET(fpcurthread) == td) {
+	if (__predict_false(PCPU_GET(fpcurthread) == td)) {
 		/*
 		 * Some virtual machines seems to set %cr0.TS at
 		 * arbitrary moments.  Silently clear the TS bit
@@ -730,15 +730,15 @@ fpudna(void)
 		 * mode.
 		 */
 		stop_emulating();
-		critical_exit();
-		return;
+	} else {
+		if (__predict_false(PCPU_GET(fpcurthread) != NULL)) {
+			panic(
+		    "fpudna: fpcurthread = %p (%d), curthread = %p (%d)\n",
+			    PCPU_GET(fpcurthread),
+			    PCPU_GET(fpcurthread)->td_tid, td, td->td_tid);
+		}
+		restore_fpu_curthread(td);
 	}
-	if (PCPU_GET(fpcurthread) != NULL) {
-		panic("fpudna: fpcurthread = %p (%d), curthread = %p (%d)\n",
-		    PCPU_GET(fpcurthread), PCPU_GET(fpcurthread)->td_tid,
-		    td, td->td_tid);
-	}
-	restore_fpu_curthread(td);
 	critical_exit();
 }
 

Modified: head/sys/i386/i386/npx.c
==============================================================================
--- head/sys/i386/i386/npx.c	Thu Jun 14 10:33:26 2018	(r335131)
+++ head/sys/i386/i386/npx.c	Thu Jun 14 11:09:51 2018	(r335132)
@@ -835,7 +835,7 @@ npxdna(void)
 		return (0);
 	td = curthread;
 	critical_enter();
-	if (PCPU_GET(fpcurthread) == td) {
+	if (__predict_false(PCPU_GET(fpcurthread) == td)) {
 		/*
 		 * Some virtual machines seems to set %cr0.TS at
 		 * arbitrary moments.  Silently clear the TS bit
@@ -843,19 +843,18 @@ npxdna(void)
 		 * mode.
 		 */
 		stop_emulating();
-		critical_exit();
-		return (1);
+	} else {
+		if (__predict_false(PCPU_GET(fpcurthread) != NULL)) {
+			printf(
+		    "npxdna: fpcurthread = %p (%d), curthread = %p (%d)\n",
+			    PCPU_GET(fpcurthread),
+			    PCPU_GET(fpcurthread)->td_proc->p_pid,
+			    td, td->td_proc->p_pid);
+			panic("npxdna");
+		}
+		restore_npx_curthread(td, td->td_pcb);
 	}
-	if (PCPU_GET(fpcurthread) != NULL) {
-		printf("npxdna: fpcurthread = %p (%d), curthread = %p (%d)\n",
-		       PCPU_GET(fpcurthread),
-		       PCPU_GET(fpcurthread)->td_proc->p_pid,
-		       td, td->td_proc->p_pid);
-		panic("npxdna");
-	}
-	restore_npx_curthread(td, td->td_pcb);
 	critical_exit();
-
 	return (1);
 }

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