----- 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.
Paolo
