Doubling the number of atomic ops was expected to cause a severe performance
regression. This hack demonstrates that the test code wasn't responsible. A
bit of extra suspicion in clib_bihash_search_inline_2_with_hash() will
likely solve the problem without the huge performance regression.
D.
-----Original Message-----
From: vpp-dev@lists.fd.io <vpp-dev@lists.fd.io> On Behalf Of Hao Tian
Sent: Tuesday, March 14, 2023 9:47 PM
To: vpp-dev@lists.fd.io
Subject: Re: [vpp-dev] Race condition between bihash deletion and searching
- misuse or bug?
Hi,
I've done the change you asked, and the "suspicious value" warnings are all
gone. Here is the diff:
diff --git a/src/vppinfra/bihash_template.h b/src/vppinfra/bihash_template.h
index c4e120e4a..b9f658db3 100644
--- a/src/vppinfra/bihash_template.h
+++ b/src/vppinfra/bihash_template.h
@@ -532,12 +532,7 @@ static inline int BV
(clib_bihash_search_inline_2_with_hash)
if (PREDICT_FALSE (BV (clib_bihash_bucket_is_empty) (b)))
return -1;
- if (PREDICT_FALSE (b->lock))
- {
- volatile BVT (clib_bihash_bucket) * bv = b;
- while (bv->lock)
- CLIB_PAUSE ();
- }
+ BV (clib_bihash_lock_bucket) (b);
v = BV (clib_bihash_get_value) (h, b->offset);
@@ -557,9 +552,11 @@ static inline int BV
(clib_bihash_search_inline_2_with_hash)
if (BV (clib_bihash_key_compare) (v->kvp[i].key, search_key->key))
{
*valuep = v->kvp[i];
+ BV (clib_bihash_unlock_bucket) (b);
return 0;
}
}
+ BV (clib_bihash_unlock_bucket) (b);
return -1;
}
Some questions regarding the change:
1. There is similar logic in clib_bihash_search_inline_with_hash. I suppose
that this change needs to be applied there as well. Am I right?
2. This patch does eliminate the race condition, but appears to introduce a
huge performance regression. The clocks in `show runtime` will double after
the change (with the 100000-ops limit removed, so the test node runs
indefinitely).
Regards,
Hao Tian
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