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Re: [Qemu-devel] [PATCH] virtio-rng: correct the default limit rate
From: |
Amos Kong |
Subject: |
Re: [Qemu-devel] [PATCH] virtio-rng: correct the default limit rate |
Date: |
Tue, 26 Nov 2013 22:23:36 +0800 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
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