- linux-user: pin multi-threaded applications to a single host cpu

OBS-URL: https://build.opensuse.org/package/show/Virtualization/qemu?expand=0&rev=92

0026-linux-user-Run-multi-threaded-code-.patch

@@ -0,0 +1,40 @@
+From f85c851986d24df8700ffe447301786fe83819d0 Mon Sep 17 00:00:00 2001
+From: Alexander Graf <agraf@suse.de>
+Date: Tue, 10 Jul 2012 20:40:55 +0200
+Subject: [PATCH] linux-user: Run multi-threaded code on a single core
+
+Running multi-threaded code can easily expose some of the fundamental
+breakages in QEMU's design. It's just not a well supported scenario.
+
+So if we pin the whole process to a single host CPU, we guarantee that
+we will never have concurrent memory access actually happen. We can still
+get scheduled away at any time, so it's no complete guarantee, but apparently
+it reduces the odds well enough to get my test cases to pass.
+
+This gets Java 1.7 working for me again on my test box.
+
+Signed-off-by: Alexander Graf <agraf@suse.de>
+---
+ linux-user/syscall.c |    9 +++++++++
+ 1 files changed, 9 insertions(+), 0 deletions(-)
+
+diff --git a/linux-user/syscall.c b/linux-user/syscall.c
+index 46e964b..b0566cd 100644
+--- a/linux-user/syscall.c
++++ b/linux-user/syscall.c
+@@ -4298,6 +4298,15 @@ static int do_fork(CPUArchState *env, unsigned int flags, abi_ulong newsp,
+         if (nptl_flags & CLONE_SETTLS)
+             cpu_set_tls (new_env, newtls);
+ 
++        /* agraf: Pin ourselves to a single CPU when running multi-threaded.
++           This turned out to improve stability for me. */
++        {
++            cpu_set_t mask;
++            CPU_ZERO(&mask);
++            CPU_SET(0, &mask);
++            sched_setaffinity(0, sizeof(mask), &mask);
++        }
++
+         /* Grab a mutex so that thread setup appears atomic.  */
+         pthread_mutex_lock(&clone_lock);
+ 

qemu.changes

@@ -1,3 +1,8 @@
+-------------------------------------------------------------------
+Tue Jul 10 18:43:31 UTC 2012 - agraf@suse.com
+
+- linux-user: pin multi-threaded applications to a single host cpu
+
 -------------------------------------------------------------------
 Tue Jul 10 16:42:54 UTC 2012 - agraf@suse.com
 

qemu.spec

@@ -49,6 +49,7 @@ Patch0022:      0022-use-libexecdir-instead-of-ignoring-.patch
 Patch0023:      0023-linux-user-Ignore-broken-loop-ioctl.patch
 Patch0024:      0024-linux-user-fix-segmentation-fault-p.patch
 Patch0025:      0025-linux-user-lock-tcg.patch.patch
+Patch0026:      0026-linux-user-Run-multi-threaded-code-.patch
 # this is to make lint happy
 Source300:      rpmlintrc
 Source302:      bridge.conf
@@ -181,6 +182,7 @@ run cross-architecture builds.
 %patch0023 -p1
 %patch0024 -p1
 %patch0025 -p1
+%patch0026 -p1
 
 %build
 # build QEMU