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From: Stefano Brivio <sbrivio@redhat.com>
To: Pablo Neira Ayuso <pablo@netfilter.org>, netfilter-devel@vger.kernel.org
Subject: [PATCH nf-next 2/2] netfilter: nft_set_pipapo: Don't abuse unlikely() in pipapo_refill()
Date: Fri, 14 Feb 2020 18:14:14 +0100
Message-ID: <5208393012d9aa0b312f503dbd1dad565e92e032.1581699548.git.sbrivio@redhat.com> (raw)
In-Reply-To: <cover.1581699548.git.sbrivio@redhat.com>

I originally used unlikely() in the if (match_only) clause, which
we hit on the mapping table for the last field in a set, to ensure
we avoid branching to the rest of for loop body, which is executed
more frequently.

However, Pablo reports, this is confusing as it gives the impression
that this is not a common case, and it's actually not the intended
usage of unlikely().

I couldn't observe any statistical difference in matching rates on
x864_64 and aarch64 without it, so just drop it.

Reported-by: Pablo Neira Ayuso <pablo@netfilter.org>
Fixes: 3c4287f62044 ("nf_tables: Add set type for arbitrary concatenation of ranges")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 net/netfilter/nft_set_pipapo.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netfilter/nft_set_pipapo.c b/net/netfilter/nft_set_pipapo.c
index 579600b39f39..feac8553f6d9 100644
--- a/net/netfilter/nft_set_pipapo.c
+++ b/net/netfilter/nft_set_pipapo.c
@@ -503,7 +503,7 @@ static int pipapo_refill(unsigned long *map, int len, int rules,
 				return -1;
 			}
 
-			if (unlikely(match_only)) {
+			if (match_only) {
 				bitmap_clear(map, i, 1);
 				return i;
 			}
-- 
2.25.0


  parent reply index

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-14 17:14 [PATCH nf-next 0/2] Two non-functional fixes for nft_set_pipapo Stefano Brivio
2020-02-14 17:14 ` [PATCH nf-next 1/2] netfilter: nft_set_pipapo: Fix mapping table example in comments Stefano Brivio
2020-02-14 17:14 ` Stefano Brivio [this message]
2020-02-14 17:33 ` [PATCH nf-next 0/2] Two non-functional fixes for nft_set_pipapo Pablo Neira Ayuso
2020-02-18 21:07 ` Pablo Neira Ayuso

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