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Re: [Qemu-devel] [PATCH v2 11/12] cpus: call cpu_update_icount on read
From: |
Alex Bennée |
Subject: |
Re: [Qemu-devel] [PATCH v2 11/12] cpus: call cpu_update_icount on read |
Date: |
Fri, 07 Apr 2017 12:35:29 +0100 |
User-agent: |
mu4e 0.9.19; emacs 25.2.13 |
Paolo Bonzini <address@hidden> 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 <address@hidden>
>> ---
>> 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
[Qemu-devel] [PATCH v2 11/12] cpus: call cpu_update_icount on read, Alex Bennée, 2017/04/05
[Qemu-devel] [PATCH v2 10/12] cpu-exec: update icount after each TB_EXIT, Alex Bennée, 2017/04/05