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25 // This is the hardware representation of the policer.
26 // To be multithread-safe, the policer is accessed through a spin-lock
27 // on the lock field. (For a policer update operation, 24B needs to be
28 // modified and this would be a challenge to do with atomic instructions.)
29 // The structure is padded so that no other data is put into the same
30 // 64B cache-line. This reduces cache-thrashing between threads.
33 // The HW TSC tick is roughly one CPU clock cycle.
34 // This is shifted to create a larger period, with a goal to be around 50usec.
35 // The period time will vary based on CPU clock speed.
36 // CPU speeds of 1Ghz to 8Ghz are targetted.
37 // The shift amount is a constant 17 bits, resulting in a period between
38 // 16usec (8Ghz CPU) and 131usec (1Ghz CPU).
39 // The token_per_period computation takes into account the clock speed.
41 // The 32-bit bucket/limit supports about 850ms of burst on a 40GE port,
42 // or 340ms on a 100GE port. If a larger burst is configured, then the
43 // programmed value is simply capped at 2^32-1. If we needed to support
44 // more than that, the bucket and limit fields could be expanded.
46 // tokens_per_period should be > 1000 to support 0.1% granularity.
47 // To support lower rates (which would not meet this requirement), the packet
48 // length, bucket, and limit values can be scaled. The scale is a power of 2
49 // so the multiplication can be implemented as a shift. The control plane
50 // computes the shift amount be the largest possible that still supports the
51 // burst size. This makes the rate accuracy as high as possible.
53 // The 64-bit last_update_time supports a 4Ghz CPU without rollover for 100
56 // The lock field should be used for a spin-lock on the struct. Alternatively,
57 // a thread index field is provided so that policed packets may be handed
58 // off to a single worker thread.
60 #define POLICER_TICKS_PER_PERIOD_SHIFT 17
61 #define POLICER_TICKS_PER_PERIOD (1 << POLICER_TICKS_PER_PERIOD_SHIFT)
66 u32 lock; // for exclusive access to the struct
68 u32 single_rate; // 1 = single rate policer, 0 = two rate policer
69 u32 color_aware; // for hierarchical policing
70 u32 scale; // power-of-2 shift amount for lower rates
75 // Fields are marked as 2R if they are only used for a 2-rate policer,
76 // and MOD if they are modified as part of the update operation.
79 u32 cir_tokens_per_period; // # of tokens for each period
80 u32 pir_tokens_per_period; // 2R
83 u32 current_bucket; // MOD
85 u32 extended_bucket; // MOD
87 u64 last_update_time; // MOD
88 u32 thread_index; // Tie policer to a thread, rather than lock
91 } policer_read_response_type_st;
93 static inline policer_result_e
94 vnet_police_packet (policer_read_response_type_st * policer,
96 policer_result_e packet_color, u64 time)
99 u64 current_tokens, extended_tokens;
100 policer_result_e result;
102 // Scale packet length to support a wide range of speeds
103 packet_length = packet_length << policer->scale;
105 // Compute the number of policer periods that have passed since the last
107 n_periods = time - policer->last_update_time;
108 policer->last_update_time = time;
110 // Since there is no background last-update-time adjustment, n_periods
111 // could grow large if the policer is idle for a long time. This could
112 // cause a 64-bit overflow when computing tokens_per_period * num_periods.
113 // It will overflow if log2(n_periods) + log2(tokens_per_period) > 64.
115 // To mitigate this, the policer configuration algorithm insures that
116 // tokens_per_period is less than 2^22, i.e. this is a 22 bit value not
117 // a 32-bit value. Thus overflow will only occur if n_periods > 64-22 or
118 // 42. 2^42 min-sized periods is 16us * 2^42, or 2 years. So this can
119 // rarely occur. If overflow does happen, the only effect will be that
120 // fewer tokens than the max burst will be added to the bucket for this
121 // packet. This constraint on tokens_per_period lets the ucode omit
122 // code to dynamically check for or prevent the overflow.
124 if (policer->single_rate)
127 // Compute number of tokens for this time period
129 policer->current_bucket + n_periods * policer->cir_tokens_per_period;
130 if (current_tokens > policer->current_limit)
132 current_tokens = policer->current_limit;
136 policer->extended_bucket + n_periods * policer->cir_tokens_per_period;
137 if (extended_tokens > policer->extended_limit)
139 extended_tokens = policer->extended_limit;
144 if ((!policer->color_aware || (packet_color == POLICE_CONFORM))
145 && (current_tokens >= packet_length))
147 policer->current_bucket = current_tokens - packet_length;
148 policer->extended_bucket = extended_tokens - packet_length;
149 result = POLICE_CONFORM;
151 else if ((!policer->color_aware || (packet_color != POLICE_VIOLATE))
152 && (extended_tokens >= packet_length))
154 policer->current_bucket = current_tokens;
155 policer->extended_bucket = extended_tokens - packet_length;
156 result = POLICE_EXCEED;
160 policer->current_bucket = current_tokens;
161 policer->extended_bucket = extended_tokens;
162 result = POLICE_VIOLATE;
170 // Compute number of tokens for this time period
172 policer->current_bucket + n_periods * policer->cir_tokens_per_period;
174 policer->extended_bucket + n_periods * policer->pir_tokens_per_period;
175 if (current_tokens > policer->current_limit)
177 current_tokens = policer->current_limit;
179 if (extended_tokens > policer->extended_limit)
181 extended_tokens = policer->extended_limit;
186 if ((policer->color_aware && (packet_color == POLICE_VIOLATE))
187 || (extended_tokens < packet_length))
189 policer->current_bucket = current_tokens;
190 policer->extended_bucket = extended_tokens;
191 result = POLICE_VIOLATE;
193 else if ((policer->color_aware && (packet_color == POLICE_EXCEED))
194 || (current_tokens < packet_length))
196 policer->current_bucket = current_tokens;
197 policer->extended_bucket = extended_tokens - packet_length;
198 result = POLICE_EXCEED;
202 policer->current_bucket = current_tokens - packet_length;
203 policer->extended_bucket = extended_tokens - packet_length;
204 result = POLICE_CONFORM;
210 #endif // __POLICE_H__
213 * fd.io coding-style-patch-verification: ON
216 * eval: (c-set-style "gnu")