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. */
--
2.11.0
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
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
----- 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
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
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~
© 2016 - 2026 Red Hat, Inc.