linux-kernel - Re: INFO: rcu detected stall in xfrm_hash

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Message-ID: <20181214162333.utlut746n3butkuf@breakpoint.cc>
Date:   Fri, 14 Dec 2018 17:23:33 +0100
From:   Florian Westphal <fw@...len.de>
To:     Christophe Gouault <christophe.gouault@...nd.com>
Cc:     Florian Westphal <fw@...len.de>, Wolfgang Walter <linux@...m.de>,
        David Miller <davem@...emloft.net>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Steffen Klassert <steffen.klassert@...unet.com>
Subject: Re: INFO: rcu detected stall in xfrm_hash_rebuild

Christophe Gouault <christophe.gouault@...nd.com> wrote:
> The main use cases I have encountered and tried to address with the
> hash-based lookup were network operator use cases:
> - a lot of dynamic /32 <=> /32 policies (protecting GTP tunnels)
> - or a lot of dynamic policies with the same prefix lengths (e.g. /16 <=> /24)
> and a few non-hashed policies stored in the linked list.

Thanks for the detailed information.

[..]

> Could you verify how the configuration time would behave in such use
> cases if the hash-based lookup was replaced by a tree-based lookup?

I won't send a patch to remove your work, at least not at this time.

In case I'd do this removal (thresholds, hash table, or both)
i will make these tests to see how large the impact is.