Re: [Qemu-devel] [PATCH] virtio-rng: correct the default limit rate

[Amos Kong]

On Tue, Nov 26, 2013 at 02:58:26PM +0100, Paolo Bonzini wrote:
> Il 26/11/2013 14:43, Amos Kong ha scritto:
> > /* Set a default rate limit of 2^47 bytes per minute or roughly 2TB/s.  If
> >  * you have an entropy source capable of generating more entropy than this
> >  * and you can pass it through via virtio-rng, then hats off to you.  Until
> >  * then, this is unlimited for all practical purposes.
> >  */
> > 
> > But the current rate is (INT64_MAX) bytes per (1 << 16) ms, it's 128,000 
> > TB/s
> 
> You are changing:
> 
> * max-bytes from 2^63 to 2^47
> 
> * period from 65536 to 60000
> 
> For a user, changing only period would have no effect, the limit rate
> would remain effectively infinite.  Changing max-bytes would give a 7%
> higher rate after your patch.

The rate will be effected when period OR max-bytes is changed.

Before patch (as documenet described): 2^47 / 65536 = 1.953125 TB/s
Applied patch:  2^47 / 600,000 = 2.1328125 TB/s

(2.1328125 - 1.953125) / 1.953125 = 0.092

It increased 9.2%, as you said, not a big deal.
 
> Not a big deal, and max-bytes is easier to explain after your patch
> (bytes/minute) than before (bytes/65536ms).
> 
> Reviewed-by: Paolo Bonzini <address@hidden>
 
Thanks for the quick feedback.

Amos