Commit a40161cb authored by Paolo Bonzini's avatar Paolo Bonzini
Browse files

membarrier: add --enable-membarrier 



Actually enable the global memory barriers if supported by the OS.
Because only recent versions of Linux include the support, they
are disabled by default.  Note that it also has to be disabled
for QEMU to run under Wine.

Before this patch, rcutorture reports 85 ns/read for my machine,
after the patch it reports 12.5 ns/read.  On the other hand updates
go from 50 *micro*seconds to 20 *milli*seconds.

Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent c8d3877e

configure

+41 −1
Original line number Diff line number Diff line
@@ -342,7 +342,7 @@ attr="" 
libattr=""

xfs=""

tcg="yes"



membarrier=""

vhost_net="no"

vhost_crypto="no"

vhost_scsi="no"
@@ -1161,6 +1161,10 @@ for opt do 
  ;;

  --enable-attr) attr="yes"

  ;;

  --disable-membarrier) membarrier="no"

  ;;

  --enable-membarrier) membarrier="yes"

  ;;

  --disable-blobs) blobs="no"

  ;;

  --with-pkgversion=*) pkgversion="$optarg"
@@ -1577,6 +1581,7 @@ disabled with --disable-FEATURE, default is enabled if available: 
  xen-pci-passthrough

  brlapi          BrlAPI (Braile)

  curl            curl connectivity

  membarrier      membarrier system call (for Linux 4.14+ or Windows)

  fdt             fdt device tree

  bluez           bluez stack connectivity

  kvm             KVM acceleration support
@@ -5137,6 +5142,37 @@ if compile_prog "" "" ; then 
    have_fsxattr=yes

fi



##########################################

# check for usable membarrier system call

if test "$membarrier" = "yes"; then

    have_membarrier=no

    if test "$mingw32" = "yes" ; then

        have_membarrier=yes

    elif test "$linux" = "yes" ; then

        cat > $TMPC << EOF

    #include <linux/membarrier.h>

    #include <sys/syscall.h>

    #include <unistd.h>

    #include <stdlib.h>

    int main(void) {

        syscall(__NR_membarrier, MEMBARRIER_CMD_QUERY, 0);

        syscall(__NR_membarrier, MEMBARRIER_CMD_SHARED, 0);

	exit(0);

    }

EOF

        if compile_prog "" "" ; then

            have_membarrier=yes

        fi

    fi

    if test "$have_membarrier" = "no"; then

      feature_not_found "membarrier" "membarrier system call not available"

    fi

else

    # Do not enable it by default even for Mingw32, because it doesn't

    # work on Wine.

    membarrier=no

fi



##########################################

# check if rtnetlink.h exists and is useful

have_rtnetlink=no
@@ -5763,6 +5799,7 @@ fi 
echo "malloc trim support $malloc_trim"

echo "RDMA support      $rdma"

echo "fdt support       $fdt"

echo "membarrier        $membarrier"

echo "preadv support    $preadv"

echo "fdatasync         $fdatasync"

echo "madvise           $madvise"
@@ -6245,6 +6282,9 @@ fi 
if test "$fdt" = "yes" ; then

  echo "CONFIG_FDT=y" >> $config_host_mak

fi

if test "$membarrier" = "yes" ; then

  echo "CONFIG_MEMBARRIER=y" >> $config_host_mak

fi

if test "$signalfd" = "yes" ; then

  echo "CONFIG_SIGNALFD=y" >> $config_host_mak

fi

include/qemu/sys_membarrier.h

+10 −0
Original line number Diff line number Diff line
@@ -9,9 +9,19 @@ 
#ifndef QEMU_SYS_MEMBARRIER_H

#define QEMU_SYS_MEMBARRIER_H 1



#ifdef CONFIG_MEMBARRIER

/* Only block reordering at the compiler level in the performance-critical

 * side.  The slow side forces processor-level ordering on all other cores

 * through a system call.

 */

extern void smp_mb_global_init(void);

extern void smp_mb_global(void);

#define smp_mb_placeholder()       barrier()

#else

/* Keep it simple, execute a real memory barrier on both sides.  */

static inline void smp_mb_global_init(void) {}

#define smp_mb_global()            smp_mb()

#define smp_mb_placeholder()       smp_mb()

#endif



#endif

util/Makefile.objs

+1 −0
Original line number Diff line number Diff line
@@ -33,6 +33,7 @@ util-obj-y += throttle.o 
util-obj-y += getauxval.o

util-obj-y += readline.o

util-obj-y += rcu.o

util-obj-$(CONFIG_MEMBARRIER) += sys_membarrier.o

util-obj-y += qemu-coroutine.o qemu-coroutine-lock.o qemu-coroutine-io.o

util-obj-y += qemu-coroutine-sleep.o

util-obj-y += coroutine-$(CONFIG_COROUTINE_BACKEND).o

util/sys_membarrier.c

0 → 100644
+50 −0
Original line number Diff line number Diff line 
/*

 * Process-global memory barriers

 *

 * Copyright (c) 2018 Red Hat, Inc.

 *

 * Author: Paolo Bonzini <pbonzini@redhat.com>

 */



#include <qemu/osdep.h>

#include <qemu/sys_membarrier.h>

#include <qemu/error-report.h>



#ifdef CONFIG_LINUX

#include <linux/membarrier.h>

#include <sys/syscall.h>



static int

membarrier(int cmd, int flags)

{

    return syscall(__NR_membarrier, cmd, flags);

}

#endif



void smp_mb_global(void)

{

#if defined CONFIG_WIN32

    FlushProcessWriteBuffers();

#elif defined CONFIG_LINUX

    membarrier(MEMBARRIER_CMD_SHARED, 0);

#else

#error --enable-membarrier is not supported on this operating system.

#endif

}



void smp_mb_global_init(void)

{

#ifdef CONFIG_LINUX

    int ret = membarrier(MEMBARRIER_CMD_QUERY, 0);

    if (ret < 0) {

        error_report("This QEMU binary requires the membarrier system call.");

        error_report("Please upgrade your system to a newer version of Linux");

        exit(1);

    }

    if (!(ret & MEMBARRIER_CMD_SHARED)) {

        error_report("This QEMU binary requires MEMBARRIER_CMD_SHARED support.");

        error_report("Please upgrade your system to a newer version of Linux");

        exit(1);

    }

#endif

}