netdev - Re: [PATCH bpf-next 3/3] bpf: convert explored

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Date:   Wed, 22 May 2019 04:18:48 +0000
From:   Alexei Starovoitov <ast@...com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        Networking <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "Kernel Team" <Kernel-team@...com>
Subject: Re: [PATCH bpf-next 3/3] bpf: convert explored_states to hash table

On 5/21/19 9:09 PM, Andrii Nakryiko wrote:
> 
>>   Hit/miss heuristic is not counting index miscompare as a miss.
>>   Otherwise verifier stats become unstable when experimenting
>>   with different hash functions.
>>
>> If insn comparison is done inside states_equal() then
>> miss > hit * 3 + 3 heuristic affects 'collisions'.
>> The cases where different indices fall into the same bucket.
>> And verifier stats fluctuate when hash function or size changes.
>>
> 
> Yeah, that make sense. I wonder if curframe comparison has similar
> effect, states from different frames seem similar to hash collisions
> between different instruction states in that regard. Or they are not?

Since curframe is not part of the hash it doesn't have such property.