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24 // This is the hardware representation of the policer.
25 // To be multithread-safe, the policer is accessed through a spin-lock
26 // on the lock field. (For a policer update operation, 24B needs to be
27 // modified and this would be a challenge to do with atomic instructions.)
28 // The structure is padded so that no other data is put into the same
29 // 64B cache-line. This reduces cache-thrashing between threads.
32 // The HW TSC tick is roughly one CPU clock cycle.
33 // This is shifted to create a larger period, with a goal to be around 50usec.
34 // The period time will vary based on CPU clock speed.
35 // CPU speeds of 1Ghz to 8Ghz are targetted.
36 // The shift amount is a constant 17 bits, resulting in a period between
37 // 16usec (8Ghz CPU) and 131usec (1Ghz CPU).
38 // The token_per_period computation takes into account the clock speed.
40 // The 32-bit bucket/limit supports about 850ms of burst on a 40GE port,
41 // or 340ms on a 100GE port. If a larger burst is configued, then the
42 // programmed value is simply capped at 2^32-1. If we needed to support
43 // more than that, the bucket and limit fields could be expanded.
45 // tokens_per_period should be > 1000 to support 0.1% granularity.
46 // To support lower rates (which would not meet this requirement), the packet
47 // length, bucket, and limit values can be scaled. The scale is a power of 2
48 // so the multiplication can be implemented as a shift. The control plane
49 // computes the shift amount be the largest possible that still supports the
50 // burst size. This makes the rate accuracy as high as possible.
52 // The 64-bit last_update_time supports a 4Ghz CPU without rollover for 100 years
54 // The lock field should be used for a spin-lock on the struct.
56 #define POLICER_TICKS_PER_PERIOD_SHIFT 17
57 #define POLICER_TICKS_PER_PERIOD (1 << POLICER_TICKS_PER_PERIOD_SHIFT)
61 uint32_t lock; // for exclusive access to the struct
63 uint32_t single_rate; // 1 = single rate policer, 0 = two rate policer
64 uint32_t color_aware; // for hierarchical policing
65 uint32_t scale; // power-of-2 shift amount for lower rates
68 // Fields are marked as 2R if they are only used for a 2-rate policer,
69 // and MOD if they are modified as part of the update operation.
72 uint32_t cir_tokens_per_period; // # of tokens for each period
73 uint32_t pir_tokens_per_period; // 2R
75 uint32_t current_limit;
76 uint32_t current_bucket; // MOD
77 uint32_t extended_limit;
78 uint32_t extended_bucket; // MOD
80 uint64_t last_update_time; // MOD
83 } policer_read_response_type_st;
85 static inline policer_result_e
86 vnet_police_packet (policer_read_response_type_st *policer,
87 uint32_t packet_length,
88 policer_result_e packet_color,
92 uint64_t current_tokens, extended_tokens;
93 policer_result_e result;
95 // Scale packet length to support a wide range of speeds
96 packet_length = packet_length << policer->scale;
98 // Compute the number of policer periods that have passed since the last
100 n_periods = time - policer->last_update_time;
101 policer->last_update_time = time;
103 // Since there is no background last-update-time adjustment, n_periods
104 // could grow large if the policer is idle for a long time. This could
105 // cause a 64-bit overflow when computing tokens_per_period * num_periods.
106 // It will overflow if log2(n_periods) + log2(tokens_per_period) > 64.
108 // To mitigate this, the policer configuration algorithm insures that
109 // tokens_per_period is less than 2^22, i.e. this is a 22 bit value not
110 // a 32-bit value. Thus overflow will only occur if n_periods > 64-22 or
111 // 42. 2^42 min-sized periods is 16us * 2^42, or 2 years. So this can
112 // rarely occur. If overflow does happen, the only effect will be that
113 // fewer tokens than the max burst will be added to the bucket for this
114 // packet. This constraint on tokens_per_period lets the ucode omit
115 // code to dynamically check for or prevent the overflow.
117 if (policer->single_rate) {
119 // Compute number of tokens for this time period
120 current_tokens = policer->current_bucket + n_periods * policer->cir_tokens_per_period;
121 if (current_tokens > policer->current_limit) {
122 current_tokens = policer->current_limit;
125 extended_tokens = policer->extended_bucket + n_periods * policer->cir_tokens_per_period;
126 if (extended_tokens > policer->extended_limit) {
127 extended_tokens = policer->extended_limit;
132 if ((!policer->color_aware || (packet_color == POLICE_CONFORM)) && (current_tokens >= packet_length)) {
133 policer->current_bucket = current_tokens - packet_length;
134 policer->extended_bucket = extended_tokens - packet_length;
135 result = POLICE_CONFORM;
136 } else if ((!policer->color_aware || (packet_color != POLICE_VIOLATE)) && (extended_tokens >= packet_length)) {
137 policer->current_bucket = current_tokens;
138 policer->extended_bucket = extended_tokens - packet_length;
139 result = POLICE_EXCEED;
141 policer->current_bucket = current_tokens;
142 policer->extended_bucket = extended_tokens;
143 result = POLICE_VIOLATE;
149 // Compute number of tokens for this time period
150 current_tokens = policer->current_bucket + n_periods * policer->cir_tokens_per_period;
151 extended_tokens = policer->extended_bucket + n_periods * policer->pir_tokens_per_period;
152 if (current_tokens > policer->current_limit) {
153 current_tokens = policer->current_limit;
155 if (extended_tokens > policer->extended_limit) {
156 extended_tokens = policer->extended_limit;
161 if ((policer->color_aware && (packet_color == POLICE_VIOLATE)) || (extended_tokens < packet_length)) {
162 policer->current_bucket = current_tokens;
163 policer->extended_bucket = extended_tokens;
164 result = POLICE_VIOLATE;
165 } else if ((policer->color_aware && (packet_color == POLICE_EXCEED)) || (current_tokens < packet_length)) {
166 policer->current_bucket = current_tokens;
167 policer->extended_bucket = extended_tokens - packet_length;
168 result = POLICE_EXCEED;
170 policer->current_bucket = current_tokens - packet_length;
171 policer->extended_bucket = extended_tokens - packet_length;
172 result = POLICE_CONFORM;
178 #endif // __POLICE_H__