netdev - Re: [PATCH net] inet: stop leaking jiffies on the wire

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Date:   Mon, 11 Nov 2019 10:24:56 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     Thiemo Nagel <tnagel@...gle.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [PATCH net] inet: stop leaking jiffies on the wire

On Mon, Nov 11, 2019 at 9:49 AM Thiemo Nagel <tnagel@...gle.com> wrote:

> Problem a) is hard -- as you mention, it may require hardware support
> to solve it fully. However the problem that I'm suggesting to address
> is b), and that likely can be solved by swapping out prandom_u32() for
> get_random_u32().
>

Make sure a server can still generates 10 millions packets per second
using this thing :)

I believe get_random_u32() is at least 5 times more expensive than
prandom_u32(),
and that is on x86 where arch_has_random() is true and rdrand
instruction can be used.

On other arches this would probably kill performance, and eat entropy
way too much.

Really this is a discussion that should be taken to random subsystem
maintainers.

We can not simply use get_random_u32() here.