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Re: [PATCH v1 06/11] configure: disable MTTCG for MIPS guests

From: Philippe Mathieu-Daudé
Subject: Re: [PATCH v1 06/11] configure: disable MTTCG for MIPS guests
Date: Mon, 23 Mar 2020 17:30:30 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0

On 3/23/20 5:15 PM, Alex Bennée wrote:
While debugging check-acceptance failures I found an instability in
the mips64el test case. Briefly the test case:

   retry.py -n 100 -c -- ./mips64el-softmmu/qemu-system-mips64el \
     -display none -vga none -serial mon:stdio \
     -machine malta -kernel ./vmlinux-4.7.0-rc1.I6400 \
     -cpu I6400 -smp 8 -vga std \
     -append "printk.time=0 clocksource=GIC console=tty0 console=ttyS0 
panic=-1" \

Reports about a 9% failure rate:

   Results summary:
   0: 91 times (91.00%), avg time 5.547 (0.45 varience/0.67 deviation)
   -6: 9 times (9.00%), avg time 3.394 (0.02 varience/0.13 deviation)
   Ran command 100 times, 91 passes

When re-run with "--accel tcg,thread=single" the instability goes

   Results summary:
   0: 100 times (100.00%), avg time 17.318 (249.76 varience/15.80 deviation)
   Ran command 100 times, 100 passes

Which seems to indicate there is some aspect of the MIPS MTTCG fixes
that has been missed. Ideally we would fix that but I'm afraid I don't
have time to investigate and am not super familiar with the
architecture anyway. In lieu of someone tracking down the failure lets
disable it for now.

Signed-off-by: Alex Bennée <address@hidden>
Acked-by: Philippe Mathieu-Daudé <address@hidden>
Cc: Aleksandar Markovic <address@hidden>
Cc: Aurelien Jarno <address@hidden>
Cc: Aleksandar Rikalo <address@hidden>

   - only drop mip64le

Reviewed-by: Philippe Mathieu-Daudé <address@hidden>

  configure | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/configure b/configure
index 4f12cd01777..a83c6450840 100755
--- a/configure
+++ b/configure
@@ -7885,7 +7885,7 @@ case "$target_name" in
-    mttcg="yes"
+    mttcg="no"
      echo "TARGET_ABI_MIPSN64=y" >> $config_target_mak

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