Paolo Bonzini <pbonz...@redhat.com> writes:
> ----- Original Message -----
>> From: "Alex Bennée" <alex.ben...@linaro.org>
>> To: "Paolo Bonzini" <pbonz...@redhat.com>
>> Cc: dovga...@ispras.ru, r...@twiddle.net, "peter maydell"
>> <peter.mayd...@linaro.org>, qemu-devel@nongnu.org,
>> mt...@greensocs.com, "fred konrad" <fred.kon...@greensocs.com>, "a rigo"
>> <a.r...@virtualopensystems.com>,
>> c...@braap.org, "bobby prani" <bobby.pr...@gmail.com>,
>> nik...@linux.vnet.ibm.com, "Peter Crosthwaite"
>> <crosthwaite.pe...@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 <pbonz...@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.ben...@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
