Re: [PATCH v2 05/14] contrib/plugins: add a scaling factor to the ips arg

["Alex Bennée" <alex.bennee@linaro.org>]

Akihiko Odaki <akihiko.odaki@daynix.com> writes:

> On 2025/05/06 21:57, Alex Bennée wrote:
>> It's easy to get lost in zeros while setting the numbers of
>> instructions per second. Add a scaling suffix to make things simpler.
>> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
>> Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
>> ---
>> v2
>>    - normalise the suffix before a full strcmp0
>>    - check endptr actually set
>>    - fix checkpatch
>> ---
>>   contrib/plugins/ips.c | 36 +++++++++++++++++++++++++++++++++++-
>>   1 file changed, 35 insertions(+), 1 deletion(-)
>> diff --git a/contrib/plugins/ips.c b/contrib/plugins/ips.c
>> index e5297dbb01..9b166a7d6c 100644
>> --- a/contrib/plugins/ips.c
>> +++ b/contrib/plugins/ips.c
>> @@ -20,6 +20,8 @@
>>     QEMU_PLUGIN_EXPORT int qemu_plugin_version =
>> QEMU_PLUGIN_VERSION;
>>   +#define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0]))
>> +
>
> G_N_ELEMENTS() is already available.
>
>>   /* how many times do we update time per sec */
>>   #define NUM_TIME_UPDATE_PER_SEC 10
>>   #define NSEC_IN_ONE_SEC (1000 * 1000 * 1000)
>> @@ -129,6 +131,18 @@ static void plugin_exit(qemu_plugin_id_t id, void *udata)
>>       qemu_plugin_scoreboard_free(vcpus);
>>   }
>>   +typedef struct {
>> +    const char *suffix;
>> +    unsigned long multipler;
>
> I prefer to have an explicitly-sized type: uint32_t in this case. It
> also saves typing several characters as a bonus.

4Ghz would be a reasonable size and that would overflow a simple
uint32_t unless we start casting.

>
>> +} scale_entry;
>
> docs/devel/style.rst says
>> Structured type names are in CamelCase; harder to type but standing
>> out.
>
>> +
>> +/* a bit like units.h but not binary */
>> +static scale_entry scales[] = {
>> +    { "khz", 1000 },
>> +    { "mhz", 1000 * 1000 },
>> +    { "ghz", 1000 * 1000 * 1000 },
>
> Having "hz" as suffixes look a bit awkard. "1 giga instructions per
> second" sounds natural, but "1 gigahertz instructions per second"
> doesn't to me. Practically, it would be easier to just type "g"
> instead of "ghz".
>
> util/cutils.c has similar code though I guess a plugin cannot be
> linked to it.
>
>> +};
>> +
>>   QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
>>                                              const qemu_info_t *info, int argc,
>>                                              char **argv)
>> @@ -137,12 +151,32 @@ QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
>>           char *opt = argv[i];
>>           g_auto(GStrv) tokens = g_strsplit(opt, "=", 2);
>>           if (g_strcmp0(tokens[0], "ips") == 0) {
>> -            max_insn_per_second = g_ascii_strtoull(tokens[1], NULL, 10);
>> +            char *endptr = NULL;
>> +            max_insn_per_second = g_ascii_strtoull(tokens[1], &endptr, 10);
>>               if (!max_insn_per_second && errno) {
>>                   fprintf(stderr, "%s: couldn't parse %s (%s)\n",
>>                           __func__, tokens[1], g_strerror(errno));
>>                   return -1;
>>               }
>> +
>> +            if (endptr && *endptr != 0) {
>> +                g_autofree gchar *lower = g_utf8_strdown(endptr, -1);
>> +                unsigned long scale = 0;
>> +
>> +                for (int j = 0; j < ARRAY_SIZE(scales); j++) {
>> +                    if (g_strcmp0(lower, scales[j].suffix) == 0) {
>> +                        scale = scales[j].multipler;
>> +                        break;
>> +                    }
>> +                }
>> +
>> +                if (scale) {
>> +                    max_insn_per_second *= scale;
>> +                } else {
>> +                    fprintf(stderr, "bad suffix: %s\n", endptr);
>> +                    return -1;
>> +                }
>> +            }
>>           } else {
>>               fprintf(stderr, "option parsing failed: %s\n", opt);
>>               return -1;

I've fixed the other cases.

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro