Re: [Qemu-devel] [PATCH 6/8] tcg/tci: disable MTTCG if TCI is enabled

[Philippe Mathieu-Daudé]

On 08/03/2017 02:56 PM, Richard Henderson wrote:

On 08/03/2017 10:40 AM, Philippe Mathieu-Daudé wrote:

On 07/26/2017 05:02 AM, Alex Bennée wrote:


Philippe Mathieu-Daudé  writes:


Hi Peter,

I think this patch belongs to 2.10, as there is no time to fix TCI +
MTTCG. Should I RESEND it alone with "for 2.10" subject?

One other option might be disable TCI if MTTCG enabled, but there is
no ./configure option for MTTCG while there is for TCI.

Regards,

Phil.

On 06/28/2017 10:02 PM, Philippe Mathieu-Daudé wrote:

TCI + MTTCG cause strange errors...

 $ arm-softmmu/qemu-system-arm -machine raspi2 -cpu cortex-a7 -smp 4
-accel tcg,thread=multi -kernel kernel7.img
 qemu-system-arm: Guest expects a stronger memory ordering than the host
provides
 This may cause strange/hard to debug errors
 Segmentation fault (core dumped)


So this isn't TCI enabling MTTCG by accident - this is the user forcing
it when it wouldn't otherwise be enabled. Hence the scary warning...


Hmmm this is the user enabling TCI, I'm not sure about "forcing it".
Now MTTCG is enforced by the ./configure and there is no option to disable it.


Er, no.

If you write "-accel tcg" you are not forcing mttcg on.
If you write "-accel tcg,thread=multi" you are forcing it on.


Ok! I obviously missed this part.


If you write "-accel tcg,thread=single" you are forcing it off.

MTTCG is only enabled by default if TCG_TARGET_DEFAULT_MO is defined, and in
the case of TCI, it is not.


Ok, so I misunderstood Alex :) I thought about ./configure enabled while 
he was describing -accel enabled.


Thanks for pointing that out :)




r~

Re: [Qemu-devel] [PATCH 6/8] tcg/tci: disable MTTCG if TCI is enabled

[Richard Henderson]

On 08/03/2017 10:40 AM, Philippe Mathieu-Daudé wrote:
> On 07/26/2017 05:02 AM, Alex Bennée wrote:
>>
>> Philippe Mathieu-Daudé  writes:
>>
>>> Hi Peter,
>>>
>>> I think this patch belongs to 2.10, as there is no time to fix TCI +
>>> MTTCG. Should I RESEND it alone with "for 2.10" subject?
>>>
>>> One other option might be disable TCI if MTTCG enabled, but there is
>>> no ./configure option for MTTCG while there is for TCI.
>>>
>>> Regards,
>>>
>>> Phil.
>>>
>>> On 06/28/2017 10:02 PM, Philippe Mathieu-Daudé wrote:
 TCI + MTTCG cause strange errors...

 $ arm-softmmu/qemu-system-arm -machine raspi2 -cpu cortex-a7 -smp 4
 -accel tcg,thread=multi -kernel kernel7.img
 qemu-system-arm: Guest expects a stronger memory ordering than the host
 provides
 This may cause strange/hard to debug errors
 Segmentation fault (core dumped)
>>
>> So this isn't TCI enabling MTTCG by accident - this is the user forcing
>> it when it wouldn't otherwise be enabled. Hence the scary warning...
> 
> Hmmm this is the user enabling TCI, I'm not sure about "forcing it".
> Now MTTCG is enforced by the ./configure and there is no option to disable it.

Er, no.

If you write "-accel tcg" you are not forcing mttcg on.
If you write "-accel tcg,thread=multi" you are forcing it on.
If you write "-accel tcg,thread=single" you are forcing it off.

MTTCG is only enabled by default if TCG_TARGET_DEFAULT_MO is defined, and in
the case of TCI, it is not.


r~

Re: [Qemu-devel] [PATCH 6/8] tcg/tci: disable MTTCG if TCI is enabled

[Philippe Mathieu-Daudé]

On 07/26/2017 05:02 AM, Alex Bennée wrote:


Philippe Mathieu-Daudé  writes:


Hi Peter,

I think this patch belongs to 2.10, as there is no time to fix TCI +
MTTCG. Should I RESEND it alone with "for 2.10" subject?

One other option might be disable TCI if MTTCG enabled, but there is
no ./configure option for MTTCG while there is for TCI.

Regards,

Phil.

On 06/28/2017 10:02 PM, Philippe Mathieu-Daudé wrote:

TCI + MTTCG cause strange errors...

$ arm-softmmu/qemu-system-arm -machine raspi2 -cpu cortex-a7 -smp 4 -accel 
tcg,thread=multi -kernel kernel7.img
qemu-system-arm: Guest expects a stronger memory ordering than the host 
provides
This may cause strange/hard to debug errors
Segmentation fault (core dumped)


So this isn't TCI enabling MTTCG by accident - this is the user forcing
it when it wouldn't otherwise be enabled. Hence the scary warning...


Hmmm this is the user enabling TCI, I'm not sure about "forcing it".
Now MTTCG is enforced by the ./configure and there is no option to 
disable it.


I posted this patch after realizing there are more TCI users/testers 
than just Stefan Weil, Jaroslaw Pelczar and me. Peter commented about 
http://qira.me/ which doesn't look very active.
(see this thread: 
http://lists.nongnu.org/archive/html/qemu-devel/2017-06/threads.html#06528 )


Thinking about eventual downstream project using the TCI part of QEMU 
and trying to stay up-to-date with upstream, this patch might save 
headaches.


Since there is no formal yes/no to this patch I'm still wondering if I 
should track it or no.


Regards,

Phil.



Signed-off-by: Philippe Mathieu-Daudé 
---
   configure | 6 +-
   1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index c571ad14e5..510f443e06 100755
--- a/configure
+++ b/configure
@@ -6225,7 +6225,11 @@ fi
   if test "$target_softmmu" = "yes" ; then
 echo "CONFIG_SOFTMMU=y" >> $config_target_mak
 if test "$mttcg" = "yes" ; then
-echo "TARGET_SUPPORTS_MTTCG=y" >> $config_target_mak
+if test "$tcg_interpreter" = "yes" ; then
+echo "TCI enabled, disabling MTTCG"
+else
+echo "TARGET_SUPPORTS_MTTCG=y" >> $config_target_mak
+fi
 fi
   fi
   if test "$target_user_only" = "yes" ; then




--
Alex Bennée

Re: [Qemu-devel] [PATCH 6/8] tcg/tci: disable MTTCG if TCI is enabled

[Alex Bennée]

Philippe Mathieu-Daudé  writes:

> Hi Peter,
>
> I think this patch belongs to 2.10, as there is no time to fix TCI +
> MTTCG. Should I RESEND it alone with "for 2.10" subject?
>
> One other option might be disable TCI if MTTCG enabled, but there is
> no ./configure option for MTTCG while there is for TCI.
>
> Regards,
>
> Phil.
>
> On 06/28/2017 10:02 PM, Philippe Mathieu-Daudé wrote:
>> TCI + MTTCG cause strange errors...
>>
>>$ arm-softmmu/qemu-system-arm -machine raspi2 -cpu cortex-a7 -smp 4 
>> -accel tcg,thread=multi -kernel kernel7.img
>>qemu-system-arm: Guest expects a stronger memory ordering than the host 
>> provides
>>This may cause strange/hard to debug errors
>>Segmentation fault (core dumped)

So this isn't TCI enabling MTTCG by accident - this is the user forcing
it when it wouldn't otherwise be enabled. Hence the scary warning...

>>
>> Signed-off-by: Philippe Mathieu-Daudé 
>> ---
>>   configure | 6 +-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/configure b/configure
>> index c571ad14e5..510f443e06 100755
>> --- a/configure
>> +++ b/configure
>> @@ -6225,7 +6225,11 @@ fi
>>   if test "$target_softmmu" = "yes" ; then
>> echo "CONFIG_SOFTMMU=y" >> $config_target_mak
>> if test "$mttcg" = "yes" ; then
>> -echo "TARGET_SUPPORTS_MTTCG=y" >> $config_target_mak
>> +if test "$tcg_interpreter" = "yes" ; then
>> +echo "TCI enabled, disabling MTTCG"
>> +else
>> +echo "TARGET_SUPPORTS_MTTCG=y" >> $config_target_mak
>> +fi
>> fi
>>   fi
>>   if test "$target_user_only" = "yes" ; then
>>


--
Alex Bennée

Re: [Qemu-devel] [PATCH 6/8] tcg/tci: disable MTTCG if TCI is enabled

[Philippe Mathieu-Daudé]

Hi Peter,

I think this patch belongs to 2.10, as there is no time to fix TCI + 
MTTCG. Should I RESEND it alone with "for 2.10" subject?


One other option might be disable TCI if MTTCG enabled, but there is no 
./configure option for MTTCG while there is for TCI.


Regards,

Phil.

On 06/28/2017 10:02 PM, Philippe Mathieu-Daudé wrote:

TCI + MTTCG cause strange errors...

   $ arm-softmmu/qemu-system-arm -machine raspi2 -cpu cortex-a7 -smp 4 -accel 
tcg,thread=multi -kernel kernel7.img
   qemu-system-arm: Guest expects a stronger memory ordering than the host 
provides
   This may cause strange/hard to debug errors
   Segmentation fault (core dumped)

Signed-off-by: Philippe Mathieu-Daudé 
---
  configure | 6 +-
  1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index c571ad14e5..510f443e06 100755
--- a/configure
+++ b/configure
@@ -6225,7 +6225,11 @@ fi
  if test "$target_softmmu" = "yes" ; then
echo "CONFIG_SOFTMMU=y" >> $config_target_mak
if test "$mttcg" = "yes" ; then
-echo "TARGET_SUPPORTS_MTTCG=y" >> $config_target_mak
+if test "$tcg_interpreter" = "yes" ; then
+echo "TCI enabled, disabling MTTCG"
+else
+echo "TARGET_SUPPORTS_MTTCG=y" >> $config_target_mak
+fi
fi
  fi
  if test "$target_user_only" = "yes" ; then

[Qemu-devel] [PATCH 6/8] tcg/tci: disable MTTCG if TCI is enabled

[Philippe Mathieu-Daudé]

TCI + MTTCG cause strange errors...

  $ arm-softmmu/qemu-system-arm -machine raspi2 -cpu cortex-a7 -smp 4 -accel 
tcg,thread=multi -kernel kernel7.img
  qemu-system-arm: Guest expects a stronger memory ordering than the host 
provides
  This may cause strange/hard to debug errors
  Segmentation fault (core dumped)

Signed-off-by: Philippe Mathieu-Daudé 
---
 configure | 6 +-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/configure b/configure
index c571ad14e5..510f443e06 100755
--- a/configure
+++ b/configure
@@ -6225,7 +6225,11 @@ fi
 if test "$target_softmmu" = "yes" ; then
   echo "CONFIG_SOFTMMU=y" >> $config_target_mak
   if test "$mttcg" = "yes" ; then
-echo "TARGET_SUPPORTS_MTTCG=y" >> $config_target_mak
+if test "$tcg_interpreter" = "yes" ; then
+echo "TCI enabled, disabling MTTCG"
+else
+echo "TARGET_SUPPORTS_MTTCG=y" >> $config_target_mak
+fi
   fi
 fi
 if test "$target_user_only" = "yes" ; then
-- 
2.13.1