[v2,11/12] cpus: call cpu_update_icount on read

Message ID 20170405132503.32125-12-alex.bennee@linaro.org
State New
Headers show
Series
  • icount and misc MTTCG fixes for 2.9-rc4
Related show

Commit Message

Alex Bennée April 5, 2017, 1:25 p.m.
This ensures each time the vCPU thread reads the icount we update the
master timer_state.qemu_icount field. This way as long as updates are
in BQL protected sections (which they should be) the main-loop can
never come to update the log and find time has gone backwards.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

---
 cpus.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

-- 
2.11.0

Comments

Paolo Bonzini April 5, 2017, 2:07 p.m. | #1
On 05/04/2017 15:25, Alex Bennée wrote:
> This ensures each time the vCPU thread reads the icount we update the

> master timer_state.qemu_icount field. This way as long as updates are

> in BQL protected sections (which they should be) the main-loop can

> never come to update the log and find time has gone backwards.

> 

> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

> ---

>  cpus.c | 6 ++----

>  1 file changed, 2 insertions(+), 4 deletions(-)

> 

> diff --git a/cpus.c b/cpus.c

> index ff75af449a..63de033cc8 100644

> --- a/cpus.c

> +++ b/cpus.c

> @@ -246,19 +246,17 @@ void cpu_update_icount(CPUState *cpu)

>  

>  int64_t cpu_get_icount_raw(void)

>  {

> -    int64_t icount;

>      CPUState *cpu = current_cpu;

>  

> -    icount = atomic_read(&timers_state.qemu_icount);

>      if (cpu && cpu->running) {

>          if (!cpu->can_do_io) {

>              fprintf(stderr, "Bad icount read\n");

>              exit(1);

>          }

>          /* Take into account what has run */

> -        icount += cpu_get_icount_executed(cpu);

> +        cpu_update_icount(cpu);

>      }

> -    return icount;

> +    return atomic_read(&timers_state.qemu_icount);

>  }

>  

>  /* Return the virtual CPU time, based on the instruction counter.  */

> 


Maybe the update should be done in gen_io_start instead.  There
shouldn't be any interference between vCPU and I/O threads except
between gen_io_start and gen_io_end.

Paolo
Alex Bennée April 7, 2017, 11:35 a.m. | #2
Paolo Bonzini <pbonzini@redhat.com> writes:

> On 05/04/2017 15:25, Alex Bennée wrote:

>> This ensures each time the vCPU thread reads the icount we update the

>> master timer_state.qemu_icount field. This way as long as updates are

>> in BQL protected sections (which they should be) the main-loop can

>> never come to update the log and find time has gone backwards.

>>

>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

>> ---

>>  cpus.c | 6 ++----

>>  1 file changed, 2 insertions(+), 4 deletions(-)

>>

>> diff --git a/cpus.c b/cpus.c

>> index ff75af449a..63de033cc8 100644

>> --- a/cpus.c

>> +++ b/cpus.c

>> @@ -246,19 +246,17 @@ void cpu_update_icount(CPUState *cpu)

>>

>>  int64_t cpu_get_icount_raw(void)

>>  {

>> -    int64_t icount;

>>      CPUState *cpu = current_cpu;

>>

>> -    icount = atomic_read(&timers_state.qemu_icount);

>>      if (cpu && cpu->running) {

>>          if (!cpu->can_do_io) {

>>              fprintf(stderr, "Bad icount read\n");

>>              exit(1);

>>          }

>>          /* Take into account what has run */

>> -        icount += cpu_get_icount_executed(cpu);

>> +        cpu_update_icount(cpu);

>>      }

>> -    return icount;

>> +    return atomic_read(&timers_state.qemu_icount);

>>  }

>>

>>  /* Return the virtual CPU time, based on the instruction counter.  */

>>

>

> Maybe the update should be done in gen_io_start instead.  There

> shouldn't be any interference between vCPU and I/O threads except

> between gen_io_start and gen_io_end.


I'm not sure I follow. gen_io_start is a translation time thing. At
least here we ensure we update whenever the value is read.


--
Alex Bennée
Paolo Bonzini April 7, 2017, 12:19 p.m. | #3
----- Original Message -----
> From: "Alex Bennée" <alex.bennee@linaro.org>

> To: "Paolo Bonzini" <pbonzini@redhat.com>

> Cc: dovgaluk@ispras.ru, rth@twiddle.net, "peter maydell" <peter.maydell@linaro.org>, qemu-devel@nongnu.org,

> mttcg@greensocs.com, "fred konrad" <fred.konrad@greensocs.com>, "a rigo" <a.rigo@virtualopensystems.com>,

> cota@braap.org, "bobby prani" <bobby.prani@gmail.com>, nikunj@linux.vnet.ibm.com, "Peter Crosthwaite"

> <crosthwaite.peter@gmail.com>

> Sent: Friday, April 7, 2017 7:35:29 PM

> Subject: Re: [PATCH v2 11/12] cpus: call cpu_update_icount on read

> 

> 

> Paolo Bonzini <pbonzini@redhat.com> writes:

> 

> > On 05/04/2017 15:25, Alex Bennée wrote:

> >> This ensures each time the vCPU thread reads the icount we update the

> >> master timer_state.qemu_icount field. This way as long as updates are

> >> in BQL protected sections (which they should be) the main-loop can

> >> never come to update the log and find time has gone backwards.

> >>

> >> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

> >> ---

> >>  cpus.c | 6 ++----

> >>  1 file changed, 2 insertions(+), 4 deletions(-)

> >>

> >> diff --git a/cpus.c b/cpus.c

> >> index ff75af449a..63de033cc8 100644

> >> --- a/cpus.c

> >> +++ b/cpus.c

> >> @@ -246,19 +246,17 @@ void cpu_update_icount(CPUState *cpu)

> >>

> >>  int64_t cpu_get_icount_raw(void)

> >>  {

> >> -    int64_t icount;

> >>      CPUState *cpu = current_cpu;

> >>

> >> -    icount = atomic_read(&timers_state.qemu_icount);

> >>      if (cpu && cpu->running) {

> >>          if (!cpu->can_do_io) {

> >>              fprintf(stderr, "Bad icount read\n");

> >>              exit(1);

> >>          }

> >>          /* Take into account what has run */

> >> -        icount += cpu_get_icount_executed(cpu);

> >> +        cpu_update_icount(cpu);

> >>      }

> >> -    return icount;

> >> +    return atomic_read(&timers_state.qemu_icount);

> >>  }

> >>

> >>  /* Return the virtual CPU time, based on the instruction counter.  */

> >>

> >

> > Maybe the update should be done in gen_io_start instead.  There

> > shouldn't be any interference between vCPU and I/O threads except

> > between gen_io_start and gen_io_end.

> 

> I'm not sure I follow. gen_io_start is a translation time thing. At

> least here we ensure we update whenever the value is read.


Sorry, I meant we should generate TCG opcodes for the translation in
gen_io_start.

Paolo
Alex Bennée April 7, 2017, 1:14 p.m. | #4
Paolo Bonzini <pbonzini@redhat.com> writes:

> ----- Original Message -----

>> From: "Alex Bennée" <alex.bennee@linaro.org>

>> To: "Paolo Bonzini" <pbonzini@redhat.com>

>> Cc: dovgaluk@ispras.ru, rth@twiddle.net, "peter maydell" <peter.maydell@linaro.org>, qemu-devel@nongnu.org,

>> mttcg@greensocs.com, "fred konrad" <fred.konrad@greensocs.com>, "a rigo" <a.rigo@virtualopensystems.com>,

>> cota@braap.org, "bobby prani" <bobby.prani@gmail.com>, nikunj@linux.vnet.ibm.com, "Peter Crosthwaite"

>> <crosthwaite.peter@gmail.com>

>> Sent: Friday, April 7, 2017 7:35:29 PM

>> Subject: Re: [PATCH v2 11/12] cpus: call cpu_update_icount on read

>>

>>

>> Paolo Bonzini <pbonzini@redhat.com> writes:

>>

>> > On 05/04/2017 15:25, Alex Bennée wrote:

>> >> This ensures each time the vCPU thread reads the icount we update the

>> >> master timer_state.qemu_icount field. This way as long as updates are

>> >> in BQL protected sections (which they should be) the main-loop can

>> >> never come to update the log and find time has gone backwards.

>> >>

>> >> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

>> >> ---

>> >>  cpus.c | 6 ++----

>> >>  1 file changed, 2 insertions(+), 4 deletions(-)

>> >>

>> >> diff --git a/cpus.c b/cpus.c

>> >> index ff75af449a..63de033cc8 100644

>> >> --- a/cpus.c

>> >> +++ b/cpus.c

>> >> @@ -246,19 +246,17 @@ void cpu_update_icount(CPUState *cpu)

>> >>

>> >>  int64_t cpu_get_icount_raw(void)

>> >>  {

>> >> -    int64_t icount;

>> >>      CPUState *cpu = current_cpu;

>> >>

>> >> -    icount = atomic_read(&timers_state.qemu_icount);

>> >>      if (cpu && cpu->running) {

>> >>          if (!cpu->can_do_io) {

>> >>              fprintf(stderr, "Bad icount read\n");

>> >>              exit(1);

>> >>          }

>> >>          /* Take into account what has run */

>> >> -        icount += cpu_get_icount_executed(cpu);

>> >> +        cpu_update_icount(cpu);

>> >>      }

>> >> -    return icount;

>> >> +    return atomic_read(&timers_state.qemu_icount);

>> >>  }

>> >>

>> >>  /* Return the virtual CPU time, based on the instruction counter.  */

>> >>

>> >

>> > Maybe the update should be done in gen_io_start instead.  There

>> > shouldn't be any interference between vCPU and I/O threads except

>> > between gen_io_start and gen_io_end.

>>

>> I'm not sure I follow. gen_io_start is a translation time thing. At

>> least here we ensure we update whenever the value is read.

>

> Sorry, I meant we should generate TCG opcodes for the translation in

> gen_io_start.


Ahh OK. I think this is 2.10 stuff though right?

>

> Paolo



--
Alex Bennée
Richard Henderson April 7, 2017, 6:42 p.m. | #5
On 04/07/2017 06:14 AM, Alex Bennée wrote:
>> Sorry, I meant we should generate TCG opcodes for the translation in

>> gen_io_start.

> Ahh OK. I think this is 2.10 stuff though right?

>


Definitely.


r~

Patch

diff --git a/cpus.c b/cpus.c
index ff75af449a..63de033cc8 100644
--- a/cpus.c
+++ b/cpus.c
@@ -246,19 +246,17 @@  void cpu_update_icount(CPUState *cpu)
 
 int64_t cpu_get_icount_raw(void)
 {
-    int64_t icount;
     CPUState *cpu = current_cpu;
 
-    icount = atomic_read(&timers_state.qemu_icount);
     if (cpu && cpu->running) {
         if (!cpu->can_do_io) {
             fprintf(stderr, "Bad icount read\n");
             exit(1);
         }
         /* Take into account what has run */
-        icount += cpu_get_icount_executed(cpu);
+        cpu_update_icount(cpu);
     }
-    return icount;
+    return atomic_read(&timers_state.qemu_icount);
 }
 
 /* Return the virtual CPU time, based on the instruction counter.  */