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Date:      Mon, 2 Dec 2019 22:34:19 +0000 (UTC)
From:      Jeff Roberson <jeff@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r355311 - head/sys/x86/x86
Message-ID:  <201912022234.xB2MYJrQ039438@repo.freebsd.org>
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Author: jeff
Date: Mon Dec  2 22:34:19 2019
New Revision: 355311
URL: https://svnweb.freebsd.org/changeset/base/355311

Log:
  Don't run sched_preempt() inside of an extra critical section.  This disables
  the sched_preempt() switch optimization and causes the sched lock to be dropped
  and immediately reacquired.
  
  Reviewed by:	jhb, kib, mav, markj (with changes)
  Differential Revision:	https://reviews.freebsd.org/D22623

Modified:
  head/sys/x86/x86/mp_x86.c

Modified: head/sys/x86/x86/mp_x86.c
==============================================================================
--- head/sys/x86/x86/mp_x86.c	Mon Dec  2 22:15:26 2019	(r355310)
+++ head/sys/x86/x86/mp_x86.c	Mon Dec  2 22:34:19 2019	(r355311)
@@ -1261,18 +1261,11 @@ ipi_bitmap_handler(struct trapframe frame)
 	int cpu = PCPU_GET(cpuid);
 	u_int ipi_bitmap;
 
-	critical_enter();
 	td = curthread;
 	td->td_intr_nesting_level++;
 	oldframe = td->td_intr_frame;
 	td->td_intr_frame = &frame;
 	ipi_bitmap = atomic_readandclear_int(&cpuid_to_pcpu[cpu]->pc_ipi_bitmap);
-	if (ipi_bitmap & (1 << IPI_PREEMPT)) {
-#ifdef COUNT_IPIS
-		(*ipi_preempt_counts[cpu])++;
-#endif
-		sched_preempt(td);
-	}
 	if (ipi_bitmap & (1 << IPI_AST)) {
 #ifdef COUNT_IPIS
 		(*ipi_ast_counts[cpu])++;
@@ -1280,14 +1273,23 @@ ipi_bitmap_handler(struct trapframe frame)
 		/* Nothing to do for AST */
 	}
 	if (ipi_bitmap & (1 << IPI_HARDCLOCK)) {
+		critical_enter();
 #ifdef COUNT_IPIS
 		(*ipi_hardclock_counts[cpu])++;
 #endif
 		hardclockintr();
+		critical_exit();
 	}
+
+	/* Run preempt after clock handlers since it may switch. */
+	if (ipi_bitmap & (1 << IPI_PREEMPT)) {
+#ifdef COUNT_IPIS
+		(*ipi_preempt_counts[cpu])++;
+#endif
+		sched_preempt(td);
+	}
 	td->td_intr_frame = oldframe;
 	td->td_intr_nesting_level--;
-	critical_exit();
 }
 
 /*

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