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Eliminate some HPACK LUTs (#26657)

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Eliminate HPACK table

Use a switch statement instead of a table lookup for the first byte of
HPACK parsing.

This will lead the way to some other improvements down the track (I have
a substantial overhaul here planned), but this is a necessary first
step.
pull/26689/head
Craig Tiller 3 years ago committed by GitHub
parent d73ec07fe7
commit 987d526efc
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2 changed files with 99 additions and 189 deletions
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  1. 201
      src/core/ext/transport/chttp2/transport/hpack_parser.cc
  2. 87
      tools/codegen/core/gen_hpack_tables.cc

201
src/core/ext/transport/chttp2/transport/hpack_parser.cc
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@ -151,107 +151,6 @@ static grpc_error_handle parse_max_tbl_size_x(grpc_chttp2_hpack_parser* p,
const uint8_t* cur,
const uint8_t* end);
/* we translate the first byte of a hpack field into one of these decoding
cases, then use a lookup table to jump directly to the appropriate parser.
_X => the integer index is all ones, meaning we need to do varint decoding
_V => the integer index is all zeros, meaning we need to decode an additional
string value */
typedef enum {
INDEXED_FIELD,
INDEXED_FIELD_X,
LITHDR_INCIDX,
LITHDR_INCIDX_X,
LITHDR_INCIDX_V,
LITHDR_NOTIDX,
LITHDR_NOTIDX_X,
LITHDR_NOTIDX_V,
LITHDR_NVRIDX,
LITHDR_NVRIDX_X,
LITHDR_NVRIDX_V,
MAX_TBL_SIZE,
MAX_TBL_SIZE_X,
ILLEGAL
} first_byte_type;
/* jump table of parse state functions -- order must match first_byte_type
above */
static const grpc_chttp2_hpack_parser_state first_byte_action[] = {
parse_indexed_field, parse_indexed_field_x, parse_lithdr_incidx,
parse_lithdr_incidx_x, parse_lithdr_incidx_v, parse_lithdr_notidx,
parse_lithdr_notidx_x, parse_lithdr_notidx_v, parse_lithdr_nvridx,
parse_lithdr_nvridx_x, parse_lithdr_nvridx_v, parse_max_tbl_size,
parse_max_tbl_size_x, parse_illegal_op};
/* indexes the first byte to a parse state function - generated by
gen_hpack_tables.c */
static const uint8_t first_byte_lut[256] = {
LITHDR_NOTIDX_V, LITHDR_NOTIDX, LITHDR_NOTIDX, LITHDR_NOTIDX,
LITHDR_NOTIDX, LITHDR_NOTIDX, LITHDR_NOTIDX, LITHDR_NOTIDX,
LITHDR_NOTIDX, LITHDR_NOTIDX, LITHDR_NOTIDX, LITHDR_NOTIDX,
LITHDR_NOTIDX, LITHDR_NOTIDX, LITHDR_NOTIDX, LITHDR_NOTIDX_X,
LITHDR_NVRIDX_V, LITHDR_NVRIDX, LITHDR_NVRIDX, LITHDR_NVRIDX,
LITHDR_NVRIDX, LITHDR_NVRIDX, LITHDR_NVRIDX, LITHDR_NVRIDX,
LITHDR_NVRIDX, LITHDR_NVRIDX, LITHDR_NVRIDX, LITHDR_NVRIDX,
LITHDR_NVRIDX, LITHDR_NVRIDX, LITHDR_NVRIDX, LITHDR_NVRIDX_X,
MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE,
MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE,
MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE,
MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE,
MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE,
MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE,
MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE,
MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE, MAX_TBL_SIZE_X,
LITHDR_INCIDX_V, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX,
LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX, LITHDR_INCIDX_X,
ILLEGAL, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD,
INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD, INDEXED_FIELD_X,
};
/* state table for huffman decoding: given a state, gives an index/16 into
next_sub_tbl. Taking that index and adding the value of the nibble being
considered returns the next state.
@ -731,7 +630,105 @@ static grpc_error_handle parse_begin(grpc_chttp2_hpack_parser* p,
return GRPC_ERROR_NONE;
}
return first_byte_action[first_byte_lut[*cur]](p, cur, end);
switch (*cur >> 4) {
// Literal header not indexed.
// First byte format: 0000xxxx
// Where xxxx:
// 0000 - literal key
// 1111 - indexed key, varint encoded index
// other - indexed key, inline encoded index
case 0:
switch (*cur & 0xf) {
case 0: // literal key
return parse_lithdr_notidx_v(p, cur, end);
case 0xf: // varint encoded key index
return parse_lithdr_notidx_x(p, cur, end);
default: // inline encoded key index
return parse_lithdr_notidx(p, cur, end);
}
// Literal header never indexed.
// First byte format: 0001xxxx
// Where xxxx:
// 0000 - literal key
// 1111 - indexed key, varint encoded index
// other - indexed key, inline encoded index
case 1:
switch (*cur & 0xf) {
case 0: // literal key
return parse_lithdr_nvridx_v(p, cur, end);
case 0xf: // varint encoded key index
return parse_lithdr_nvridx_x(p, cur, end);
default: // inline encoded key index
return parse_lithdr_nvridx(p, cur, end);
}
// Update max table size.
// First byte format: 001xxxxx
// Where xxxxx:
// 11111 - max size is varint encoded
// other - max size is stored inline
case 2:
// inline encoded max table size
return parse_max_tbl_size(p, cur, end);
case 3:
if (*cur == 0x3f) {
// varint encoded max table size
return parse_max_tbl_size_x(p, cur, end);
} else {
// inline encoded max table size
return parse_max_tbl_size(p, cur, end);
}
// Literal header with incremental indexing.
// First byte format: 01xxxxxx
// Where xxxxxx:
// 000000 - literal key
// 111111 - indexed key, varint encoded index
// other - indexed key, inline encoded index
case 4:
if (*cur == 0x40) {
// literal key
return parse_lithdr_incidx_v(p, cur, end);
}
case 5:
case 6:
// inline encoded key index
return parse_lithdr_incidx(p, cur, end);
case 7:
if (*cur == 0x7f) {
// varint encoded key index
return parse_lithdr_incidx_x(p, cur, end);
} else {
// inline encoded key index
return parse_lithdr_incidx(p, cur, end);
}
// Indexed Header Field Representation
// First byte format: 1xxxxxxx
// Where xxxxxxx:
// 0000000 - illegal
// 1111111 - varint encoded field index
// other - inline encoded field index
case 8:
if (*cur == 0x80) {
// illegal value.
return parse_illegal_op(p, cur, end);
}
case 9:
case 10:
case 11:
case 12:
case 13:
case 14:
// inline encoded field index
return parse_indexed_field(p, cur, end);
case 15:
if (*cur == 0xff) {
// varint encoded field index
return parse_indexed_field_x(p, cur, end);
} else {
// inline encoded field index
return parse_indexed_field(p, cur, end);
}
}
GPR_UNREACHABLE_CODE(abort());
}
/* stream dependency and prioritization data: we just skip it */

87
tools/codegen/core/gen_hpack_tables.cc
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@ -26,92 +26,6 @@
#include <grpc/support/log.h>
#include "src/core/ext/transport/chttp2/transport/huffsyms.h"
/*
* first byte LUT generation
*/
typedef struct {
const char *call;
/* bit prefix for the field type */
unsigned char prefix;
/* length of the bit prefix for the field type */
unsigned char prefix_length;
/* index value: 0 = all zeros, 2 = all ones, 1 otherwise */
unsigned char index;
} spec;
static const spec fields[] = {
{"INDEXED_FIELD", 0X80, 1, 1}, {"INDEXED_FIELD_X", 0X80, 1, 2},
{"LITHDR_INCIDX", 0X40, 2, 1}, {"LITHDR_INCIDX_X", 0X40, 2, 2},
{"LITHDR_INCIDX_V", 0X40, 2, 0}, {"LITHDR_NOTIDX", 0X00, 4, 1},
{"LITHDR_NOTIDX_X", 0X00, 4, 2}, {"LITHDR_NOTIDX_V", 0X00, 4, 0},
{"LITHDR_NVRIDX", 0X10, 4, 1}, {"LITHDR_NVRIDX_X", 0X10, 4, 2},
{"LITHDR_NVRIDX_V", 0X10, 4, 0}, {"MAX_TBL_SIZE", 0X20, 3, 1},
{"MAX_TBL_SIZE_X", 0X20, 3, 2},
};
static const int num_fields = sizeof(fields) / sizeof(*fields);
static unsigned char prefix_mask(unsigned char prefix_len) {
unsigned char i;
unsigned char out = 0;
for (i = 0; i < prefix_len; i++) {
/* NB: the following integer arithmetic operation needs to be in its
* expanded form due to the "integral promotion" performed (see section
* 3.2.1.1 of the C89 draft standard). A cast to the smaller container type
* is then required to avoid the compiler warning */
out = (unsigned char)(out | (unsigned char)(1 << (7 - i)));
}
return out;
}
static unsigned char suffix_mask(unsigned char prefix_len) {
return (unsigned char)~prefix_mask(prefix_len);
}
static void generate_first_byte_lut(void) {
int i, j, n;
const spec *chrspec;
unsigned char suffix;
n = printf("static CALLTYPE first_byte[256] = {");
/* for each potential first byte of a header */
for (i = 0; i < 256; i++) {
/* find the field type that matches it */
chrspec = NULL;
for (j = 0; j < num_fields; j++) {
if ((prefix_mask(fields[j].prefix_length) & i) == fields[j].prefix) {
/* NB: the following integer arithmetic operation needs to be in its
* expanded form due to the "integral promotion" performed (see section
* 3.2.1.1 of the C89 draft standard). A cast to the smaller container
* type is then required to avoid the compiler warning */
suffix = (unsigned char)(suffix_mask(fields[j].prefix_length) &
(unsigned char)i);
if (suffix == suffix_mask(fields[j].prefix_length)) {
if (fields[j].index != 2) continue;
} else if (suffix == 0) {
if (fields[j].index != 0) continue;
} else {
if (fields[j].index != 1) continue;
}
GPR_ASSERT(chrspec == NULL);
chrspec = &fields[j];
}
}
if (chrspec) {
n += printf("%s, ", chrspec->call);
} else {
n += printf("ILLEGAL, ");
}
/* make some small effort towards readable output */
if (n > 70) {
printf("\n ");
n = 2;
}
}
printf("};\n");
}
/*
* Huffman decoder table generation
*/
@ -327,7 +241,6 @@ static void generate_base64_huff_encoder_table(void) {
int main(void) {
generate_huff_tables();
generate_first_byte_lut();
generate_base64_huff_encoder_table();
return 0;

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