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7 * http://www.apache.org/licenses/LICENSE-2.0
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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 configued, 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 years
55 // The lock field should be used for a spin-lock on the struct.
57 #define POLICER_TICKS_PER_PERIOD_SHIFT 17
58 #define POLICER_TICKS_PER_PERIOD (1 << POLICER_TICKS_PER_PERIOD_SHIFT)
63 u32 lock; // for exclusive access to the struct
65 u32 single_rate; // 1 = single rate policer, 0 = two rate policer
66 u32 color_aware; // for hierarchical policing
67 u32 scale; // power-of-2 shift amount for lower rates
72 // Fields are marked as 2R if they are only used for a 2-rate policer,
73 // and MOD if they are modified as part of the update operation.
76 u32 cir_tokens_per_period; // # of tokens for each period
77 u32 pir_tokens_per_period; // 2R
80 u32 current_bucket; // MOD
82 u32 extended_bucket; // MOD
84 u64 last_update_time; // MOD
87 } policer_read_response_type_st;
89 static inline policer_result_e
90 vnet_police_packet (policer_read_response_type_st * policer,
92 policer_result_e packet_color, u64 time)
95 u64 current_tokens, extended_tokens;
96 policer_result_e result;
98 // Scale packet length to support a wide range of speeds
99 packet_length = packet_length << policer->scale;
101 // Compute the number of policer periods that have passed since the last
103 n_periods = time - policer->last_update_time;
104 policer->last_update_time = time;
106 // Since there is no background last-update-time adjustment, n_periods
107 // could grow large if the policer is idle for a long time. This could
108 // cause a 64-bit overflow when computing tokens_per_period * num_periods.
109 // It will overflow if log2(n_periods) + log2(tokens_per_period) > 64.
111 // To mitigate this, the policer configuration algorithm insures that
112 // tokens_per_period is less than 2^22, i.e. this is a 22 bit value not
113 // a 32-bit value. Thus overflow will only occur if n_periods > 64-22 or
114 // 42. 2^42 min-sized periods is 16us * 2^42, or 2 years. So this can
115 // rarely occur. If overflow does happen, the only effect will be that
116 // fewer tokens than the max burst will be added to the bucket for this
117 // packet. This constraint on tokens_per_period lets the ucode omit
118 // code to dynamically check for or prevent the overflow.
120 if (policer->single_rate)
123 // Compute number of tokens for this time period
125 policer->current_bucket + n_periods * policer->cir_tokens_per_period;
126 if (current_tokens > policer->current_limit)
128 current_tokens = policer->current_limit;
132 policer->extended_bucket + n_periods * policer->cir_tokens_per_period;
133 if (extended_tokens > policer->extended_limit)
135 extended_tokens = policer->extended_limit;
140 if ((!policer->color_aware || (packet_color == POLICE_CONFORM))
141 && (current_tokens >= packet_length))
143 policer->current_bucket = current_tokens - packet_length;
144 policer->extended_bucket = extended_tokens - packet_length;
145 result = POLICE_CONFORM;
147 else if ((!policer->color_aware || (packet_color != POLICE_VIOLATE))
148 && (extended_tokens >= packet_length))
150 policer->current_bucket = current_tokens;
151 policer->extended_bucket = extended_tokens - packet_length;
152 result = POLICE_EXCEED;
156 policer->current_bucket = current_tokens;
157 policer->extended_bucket = extended_tokens;
158 result = POLICE_VIOLATE;
166 // Compute number of tokens for this time period
168 policer->current_bucket + n_periods * policer->cir_tokens_per_period;
170 policer->extended_bucket + n_periods * policer->pir_tokens_per_period;
171 if (current_tokens > policer->current_limit)
173 current_tokens = policer->current_limit;
175 if (extended_tokens > policer->extended_limit)
177 extended_tokens = policer->extended_limit;
182 if ((policer->color_aware && (packet_color == POLICE_VIOLATE))
183 || (extended_tokens < packet_length))
185 policer->current_bucket = current_tokens;
186 policer->extended_bucket = extended_tokens;
187 result = POLICE_VIOLATE;
189 else if ((policer->color_aware && (packet_color == POLICE_EXCEED))
190 || (current_tokens < packet_length))
192 policer->current_bucket = current_tokens;
193 policer->extended_bucket = extended_tokens - packet_length;
194 result = POLICE_EXCEED;
198 policer->current_bucket = current_tokens - packet_length;
199 policer->extended_bucket = extended_tokens - packet_length;
200 result = POLICE_CONFORM;
206 #endif // __POLICE_H__
209 * fd.io coding-style-patch-verification: ON
212 * eval: (c-set-style "gnu")