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lib/classifier: Clarify subtable skipping.

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Clarify comments for trie-based subtable skipping.

Perform the cheaper check first.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
Acked-by: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
This commit is contained in:
Jarno Rajahalme
2014-07-18 02:24:27 -07:00
parent c0bfb6502c
commit 1817dceab1
1 changed files with 12 additions and 14 deletions
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26
lib/classifier.c
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@@ -1445,27 +1445,25 @@ check_tries(struct trie_ctx trie_ctx[CLS_MAX_TRIES], unsigned int n_tries,
/* Possible to skip the rest of the subtable if subtable's
* prefix on the field is not included in the lookup result. */
if (!be_get_bit_at(&ctx->match_plens.be32, field_plen[j] - 1)) {
/* RFC: We want the trie lookup to never result in
* unwildcarding any bits that would not be unwildcarded
* otherwise. Since the trie is shared by the whole
* classifier, it is possible that the 'maskbits' contain
* bits that are irrelevant for the partition of the
* classifier relevant for the current flow. */
/* We want the trie lookup to never result in unwildcarding
* any bits that would not be unwildcarded otherwise.
* Since the trie is shared by the whole classifier, it is
* possible that the 'maskbits' contain bits that are
* irrelevant for the partition relevant for the current
* packet. Hence the checks below. */
/* Can skip if the field is already unwildcarded. */
if (mask_prefix_bits_set(wc, be32ofs, ctx->maskbits)) {
return true;
}
/* Check that the trie result will not unwildcard more bits
* than this stage will. */
* than this subtable would otherwise. */
if (ctx->maskbits <= field_plen[j]) {
/* Unwildcard the bits and skip the rest. */
mask_set_prefix_bits(wc, be32ofs, ctx->maskbits);
/* Note: Prerequisite already unwildcarded, as the only
* prerequisite of the supported trie lookup fields is
* the ethertype, which is currently always
* unwildcarded.
*/
* the ethertype, which is always unwildcarded. */
return true;
}
/* Can skip if the field is already unwildcarded. */
if (mask_prefix_bits_set(wc, be32ofs, ctx->maskbits)) {
return true;
}
}