[ovs-dev] [PATCH] dpif-netdev: Add core id in the PMD thread name.

[Ilya Maximets]

On 13.08.2019 19:46, Eelco Chaudron wrote:
> 
> 
> On 13 Aug 2019, at 18:37, Ilya Maximets wrote:
> 
>> This is highly useful to see on which core PMD is running by
>> only looking at the thread name. Thread Id still allows to
>> distinguish different threads running on the same core over the time:
>>
>>    |dpif_netdev(pmd-c10/id:53)|DBG|Creating 2. subtable <...>
>>    |dpif_netdev(pmd-c10/id:53)|DBG|flow_add: <...>, actions:2
>>    |dpif_netdev(pmd-c09/id:70)|DBG|Core 9 processing port <..>
>>
>> In gdb, top or any other utility it's useful to quickly catch up
>> needed thread without parsing logs, memory or matching threads by port
>> names they're handling.
>>
>> Signed-off-by: Ilya Maximets <i.maximets at samsung.com>
>> ---
>>  lib/dpif-netdev.c | 9 ++++++++-
>>  1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
>> index d0a1c58ad..34ba03836 100644
>> --- a/lib/dpif-netdev.c
>> +++ b/lib/dpif-netdev.c
>> @@ -4735,9 +4735,16 @@ reconfigure_pmd_threads(struct dp_netdev *dp)
>>      FOR_EACH_CORE_ON_DUMP(core, pmd_cores) {
>>          pmd = dp_netdev_get_pmd(dp, core->core_id);
>>          if (!pmd) {
>> +            struct ds name = DS_EMPTY_INITIALIZER;
>> +
>>              pmd = xzalloc(sizeof *pmd);
>>              dp_netdev_configure_pmd(pmd, dp, core->core_id, core->numa_id);
>> -            pmd->thread = ovs_thread_create("pmd", pmd_thread_main, pmd);
>> +
>> +            ds_put_format(&name, "pmd-c%02d/id:", core->core_id);
> 
> This is a really good idea :) One remark should we make it %03d?

There is a hard limit for the thread name. It's 15 meaningful chars excluding the
terminating null byte. 'pmd-c02/id:' is 11 bytes wide keeping 4 bytes for the
thread id. 'pmd-c002/id:' is 12 bytes wide with only 3 bytes remaining for id.
Thread ids could easily become big ( > 1000) for a long running process, that is
why %02d was chosen, to save some space.

BTW, even on a systems with 100+ CPUs I'm usually placing OVS threads on a lower
cores. Anyway, this is only the matter of a bit more visual beauty in the logs.

What do you think?

> 
>> +            pmd->thread = ovs_thread_create(ds_cstr(&name),
>> +                                            pmd_thread_main, pmd);
>> +            ds_destroy(&name);
>> +
>>              VLOG_INFO("PMD thread on numa_id: %d, core id: %2d created.",
>>                        pmd->numa_id, pmd->core_id);
>>              changed = true;
>> -- 
>> 2.17.1
> 
>