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membarrier: add --enable-membarrier

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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: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2018-02-16 10:05:23 +01:00
parent c8d3877e48
commit a40161cbe9
4 changed files with 102 additions and 1 deletions
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42
configure vendored
View file

@ -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