[Cake] options for shrinking cake xstats

Dave Taht dave.taht at gmail.com
Tue Dec 5 19:06:18 EST 2017

as 1400+ bytes on the parisc stack, is a bit much. That said, I don't
see much possibility for shrinkage overall.

A) if we resort to having a struct new_cake_xstats[q->tin_cnt], we
still end up with a big stack on the diffserv8 case (that won't get
caught by a static checker)

B) I'm on record as disliking any statistics calculation that is not
directly needed by the algorithm. Putting my asbestos suit on, that's
peak_delay_us, avge_delay_us, base_delay_us, way_indirect_hits,
way_misses, way_collisions, bulk_flow_count, and a few others.

C) Can we return a tuple to tc saying "we have 8 queues, poll me for each"?

D) Put the extended stats in sysfs, instead?

E) ??

struct tc_cake_traffic_stats {
        __u32 packets;
        __u32 link_ms; // essentially unused, but we could promote
packets to u64.
        __u64 bytes;

#define TC_CAKE_MAX_TINS (8)
struct tc_cake_xstats {
        __u16 version;  /* == 5, increments when struct extended */
        __u8  max_tins; /* == TC_CAKE_MAX_TINS */
        __u8  tin_cnt;  /* <= TC_CAKE_MAX_TINS */

        __u32 threshold_rate[TC_CAKE_MAX_TINS];
        __u32 target_us[TC_CAKE_MAX_TINS];
        struct tc_cake_traffic_stats sent[TC_CAKE_MAX_TINS];
        struct tc_cake_traffic_stats dropped[TC_CAKE_MAX_TINS];
        struct tc_cake_traffic_stats ecn_marked[TC_CAKE_MAX_TINS];
        struct tc_cake_traffic_stats backlog[TC_CAKE_MAX_TINS];
        __u32 interval_us[TC_CAKE_MAX_TINS];
        __u32 way_indirect_hits[TC_CAKE_MAX_TINS];
        __u32 way_misses[TC_CAKE_MAX_TINS];
        __u32 way_collisions[TC_CAKE_MAX_TINS];
        __u32 peak_delay_us[TC_CAKE_MAX_TINS]; /* ~= bulk flow delay */
        __u32 avge_delay_us[TC_CAKE_MAX_TINS];
        __u32 base_delay_us[TC_CAKE_MAX_TINS]; /* ~= sparse flows delay */
        __u16 sparse_flows[TC_CAKE_MAX_TINS];
        __u16 bulk_flows[TC_CAKE_MAX_TINS];
        __u16 unresponse_flows[TC_CAKE_MAX_TINS]; /* v4 - was u32 last_len */
        __u16 spare[TC_CAKE_MAX_TINS]; /* v4 - split last_len */
        __u32 max_skblen[TC_CAKE_MAX_TINS];
        __u32 capacity_estimate;  /* version 2 */
        __u32 memory_limit;       /* version 3 */
        __u32 memory_used;        /* version 3 */
        struct tc_cake_traffic_stats ack_drops[TC_CAKE_MAX_TINS]; /* v5 */


Dave Täht
CEO, TekLibre, LLC
Tel: 1-669-226-2619

More information about the Cake mailing list