Re: [PATCH v1] sched: enable/disable TC OV at runtime

[Stephen Hemminger <stephen@networkplumber.org>]

On Thu, 10 Mar 2022 19:54:26 +0000
Megha Ajmera <megha.ajmera@intel.com> wrote:

> diff --git a/lib/sched/rte_sched.c b/lib/sched/rte_sched.c
> index ec74bee939..1d05089d00 100644
> --- a/lib/sched/rte_sched.c
> +++ b/lib/sched/rte_sched.c
> @@ -155,6 +155,7 @@ struct rte_sched_subport {
>  	uint64_t tc_credits[RTE_SCHED_TRAFFIC_CLASSES_PER_PIPE];
>  
>  	/* TC oversubscription */
> +	uint8_t is_tc_ov_enabled;
>  	uint64_t tc_ov_wm;
>  	uint64_t tc_ov_wm_min;
>  	uint64_t tc_ov_wm_max;

Putting the field there creates a hole in the structure.
Put it after tc_ov and fill an existing hole.

This is pahole of current code, looks like this struct could
use some work to be better packed and aligned.

struct rte_sched_port {
	uint32_t                   n_subports_per_port;  /*     0     4 */
	uint32_t                   n_pipes_per_subport;  /*     4     4 */
	uint32_t                   n_pipes_per_subport_log2; /*     8     4 */
	uint16_t                   pipe_queue[13];       /*    12    26 */
	uint8_t                    pipe_tc[16];          /*    38    16 */
	uint8_t                    tc_queue[16];         /*    54    16 */

	/* XXX 2 bytes hole, try to pack */

	/* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
	uint32_t                   n_subport_profiles;   /*    72     4 */
	uint32_t                   n_max_subport_profiles; /*    76     4 */
	uint64_t                   rate;                 /*    80     8 */
	uint32_t                   mtu;                  /*    88     4 */
	uint32_t                   frame_overhead;       /*    92     4 */
	int                        socket;               /*    96     4 */

	/* XXX 4 bytes hole, try to pack */

	uint64_t                   time_cpu_cycles;      /*   104     8 */
	uint64_t                   time_cpu_bytes;       /*   112     8 */
	uint64_t                   time;                 /*   120     8 */
	/* --- cacheline 2 boundary (128 bytes) --- */
	struct rte_reciprocal      inv_cycles_per_byte;  /*   128     8 */

	/* XXX last struct has 2 bytes of padding */

	uint64_t                   cycles_per_byte;      /*   136     8 */
	struct rte_mbuf * *        pkts_out;             /*   144     8 */
	uint32_t                   n_pkts_out;           /*   152     4 */
	uint32_t                   subport_id;           /*   156     4 */
	struct rte_sched_subport_profile * subport_profiles; /*   160     8 */

	/* XXX 24 bytes hole, try to pack */

	/* --- cacheline 3 boundary (192 bytes) --- */
	struct rte_sched_subport * subports[] __attribute__((__aligned__(64))); /*   192     0 */

	/* size: 192, cachelines: 3, members: 22 */
	/* sum members: 162, holes: 3, sum holes: 30 */
	/* paddings: 1, sum paddings: 2 */
	/* forced alignments: 1, forced holes: 1, sum forced holes: 24 */
} __attribute__((__aligned__(64)));