Re: [Qemu-devel] Re: [PATCH] flush TB on singlestep command

[Alexander Graf]

On 20.04.2010, at 09:18, Jan Kiszka wrote:

> Jun Koi wrote:
>> Thank you for the explanation of this code.
>> 
>> Qemu has a command named singlestep, which reduces the translated code
>> block to be only one instruction.
>> This new patch flushes TBs both when singlestep is on and off.
>> 
>> Signed-off-by: Jun Koi <address@hidden>
>> 
>> 
>> diff --git a/monitor.c b/monitor.c
>> index 5659991..2b2005b 100644
>> --- a/monitor.c
>> +++ b/monitor.c
>> @@ -1187,13 +1187,26 @@ static void do_log(Monitor *mon, const QDict *qdict)
>>     cpu_set_log(mask);
>> }
>> 
>> +/* flush all the TBs to force new code generation */
>> +static void flush_all_tb(void)
>> +{
>> +    CPUState *env;
>> +
>> +    for (env = first_cpu; env != NULL; env = env->next_cpu) {
>> +        tb_flush(env);
>> +    }
>> +}
>> +
> 
> The smaller your patch are, the more people pick on it. :)
> 
> I was about to suggest moving this close to tb_flush, but then I
> realized that the env argument of that service is misleading. In fact,
> it already flushes the one and only translation buffer pool.
> 
>> static void do_singlestep(Monitor *mon, const QDict *qdict)
>> {
>>     const char *option = qdict_get_try_str(qdict, "option");
>> +
>>     if (!option || !strcmp(option, "on")) {
>>         singlestep = 1;
>> +        flush_all_tb();
>>     } else if (!strcmp(option, "off")) {
>>         singlestep = 0;
>> +        flush_all_tb();
>>     } else {
>>         monitor_printf(mon, "unexpected option %s\n", option);
>>     }
>> 
> 
> Let's just pass mon->mon_cpu to tb_flush and skip the redundant loop.

That doesn't help, no? singlestep is a global variable. Flushing only the 
current vcpu would still not affect the others, while the singlestep switch 
would.

According to your above comment the cache is global, but I don't think we 
should rely on that.


Alex