Re: [dpdk-dev] [PATCH] eal/linuxapp: Add parameter to specify master lcore id

[Simon Kuenzer <simon.kuenzer@neclab.eu>]

Here are some comments about the use case of this patch:

This patch is especially useful in cases where DPDK applications scale 
their CPU resources at runtime via starting and stopping slave lcores. 
Since the coremask defines the maximum scale-out for such a application, 
the master lcore becomes to the minimum scale-in.
Imagine, running multiple primary processed of such DPDK applications, 
users might want to overlap the coremasks for scaling. However, it would 
still make sense to run the master lcores on different CPU cores.

In DPDK vSwitch we might end up in such a scenario with a future release:
   https://lists.01.org/pipermail/dpdk-ovs/2014-March/000770.html
   https://lists.01.org/pipermail/dpdk-ovs/2014-March/000773.html

Thanks,

Simon

On 08.07.2014 10:28, Simon Kuenzer wrote:
> This commit enables users to specify the lcore id that
> is used as master lcore.
>
> Signed-off-by: Simon Kuenzer <simon.kuenzer@neclab.eu>
> ---
>   lib/librte_eal/linuxapp/eal/eal.c |   33 +++++++++++++++++++++++++++++++++
>   1 file changed, 33 insertions(+)
>
> diff --git a/lib/librte_eal/linuxapp/eal/eal.c b/lib/librte_eal/linuxapp/eal/eal.c
> index 573fd06..4ad5b9b 100644
> --- a/lib/librte_eal/linuxapp/eal/eal.c
> +++ b/lib/librte_eal/linuxapp/eal/eal.c
> @@ -101,6 +101,7 @@
>   #define OPT_XEN_DOM0    "xen-dom0"
>   #define OPT_CREATE_UIO_DEV "create-uio-dev"
>   #define OPT_VFIO_INTR    "vfio-intr"
> +#define OPT_MASTER_LCORE "master-lcore"
>
>   #define RTE_EAL_BLACKLIST_SIZE	0x100
>
> @@ -336,6 +337,7 @@ eal_usage(const char *prgname)
>   	       "[--proc-type primary|secondary|auto] \n\n"
>   	       "EAL options:\n"
>   	       "  -c COREMASK  : A hexadecimal bitmask of cores to run on\n"
> +	       "  --"OPT_MASTER_LCORE" ID: Core ID that is used as master\n"
>   	       "  -n NUM       : Number of memory channels\n"
>   		   "  -v           : Display version information on startup\n"
>   	       "  -d LIB.so    : add driver (can be used multiple times)\n"
> @@ -468,6 +470,21 @@ eal_parse_coremask(const char *coremask)
>   	return 0;
>   }
>
> +/* Changes the lcore id of the master thread */
> +static int
> +eal_parse_master_lcore(const char *arg)
> +{
> +	struct rte_config *cfg = rte_eal_get_configuration();
> +	int master_lcore = atoi(arg);
> +
> +	if (!(master_lcore >= 0 && master_lcore < RTE_MAX_LCORE))
> +		return -1;
> +	if (cfg->lcore_role[master_lcore] != ROLE_RTE)
> +		return -1;
> +	cfg->master_lcore = master_lcore;
> +	return 0;
> +}
> +
>   static int
>   eal_parse_syslog(const char *facility)
>   {
> @@ -653,6 +670,7 @@ eal_parse_args(int argc, char **argv)
>   		{OPT_HUGE_DIR, 1, 0, 0},
>   		{OPT_NO_SHCONF, 0, 0, 0},
>   		{OPT_PROC_TYPE, 1, 0, 0},
> +		{OPT_MASTER_LCORE, 1, 0, 0},
>   		{OPT_FILE_PREFIX, 1, 0, 0},
>   		{OPT_SOCKET_MEM, 1, 0, 0},
>   		{OPT_PCI_WHITELIST, 1, 0, 0},
> @@ -802,6 +820,21 @@ eal_parse_args(int argc, char **argv)
>   			else if (!strcmp(lgopts[option_index].name, OPT_PROC_TYPE)) {
>   				internal_config.process_type = eal_parse_proc_type(optarg);
>   			}
> +			else if (!strcmp(lgopts[option_index].name, OPT_MASTER_LCORE)) {
> +				if (!coremask_ok) {
> +					RTE_LOG(ERR, EAL, "please specify the master "
> +							"lcore id after specifying "
> +							"the coremask\n");
> +					eal_usage(prgname);
> +					return -1;
> +				}
> +				if (eal_parse_master_lcore(optarg) < 0) {
> +					RTE_LOG(ERR, EAL, "invalid parameter for --"
> +							OPT_MASTER_LCORE "\n");
> +					eal_usage(prgname);
> +					return -1;
> +				}
> +			}
>   			else if (!strcmp(lgopts[option_index].name, OPT_FILE_PREFIX)) {
>   				internal_config.hugefile_prefix = optarg;
>   			}
>