Re: [Qemu-devel] [PATCH v2 4/4] libqos/ahci: Swap memread/write with bufread/write

[John Snow]

On 05/01/2015 04:48 PM, Paolo Bonzini wrote:
> On 01/05/2015 21:55, John Snow wrote:
> > Where it makes sense, use the new faster primitives.
> > For generally small reads/writes such as for the PRDT
> > and FIS packets, stick with the more wasteful but
> > easier to debug memread/memwrite.
> >
> > For ahci-test;
> > With this patch:
> > real    0m4.802s
> > user    0m3.506s
> > sys     0m2.393s
> >
> > Without this series:
> > real    0m14.171s
> > user    0m12.072s
> > sys     0m12.527s
>
> The overhead of memread is 2, the overhead of base64 is 1.33, also
> base64 should have a larger cost of computing each byte.  It doesn't add up.

Right, there's more at play here than just the wire length.

> Could it be simply that calling qtest_send (and hence
> vsnprintf+qemu_chr_fe_write_all, neither of which are speed demons) once
> per byte is hideously inefficient? :)

I can batch those too in another patch,
or should I consider this a NACK?

> Paolo

--js