linux-kernel - Re: [PATCH] wireguard: convert index_hashtable and pubkey

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Date:   Wed, 08 Sep 2021 21:56:12 -0400
From:   Hamza Mahfooz <someguy@...ective-light.com>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        WireGuard mailing list <wireguard@...ts.zx2c4.com>,
        Netdev <netdev@...r.kernel.org>, Thomas Graf <tgraf@...g.ch>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: Re: [PATCH] wireguard: convert index_hashtable and pubkey_hashtable
 into rhashtables

Hey Jason,
On Wed, Sep 8 2021 at 01:27:12 PM +0200, Jason A. Donenfeld 
<Jason@...c4.com> wrote:
> - What's performance like? Does the abstraction of rhashtable
> introduce overhead? These are used in fast paths -- for every packet
> -- so being quick is important.

Are you familiar with any (micro)benchmarks (for WireGuard) that, you
believe would be particularly informative in assessing the outlined
performance characteristics?

> - How does this interact with the timing side channel concerns in the
> comment of the file? Will the time required to find an unused index
> leak the number of items in the hash table? Do we need stochastic
> masking? Or is the construction of rhashtable such that we always get
> ball-park same time?

I think the maintainers of rhashtable are best positioned to answer 
these
questions (I have cc'd them).