[dpdk-dev] [PATCH 06/10] Alternate implementation of librte_power for VM Power Management(Guest).

[Carew, Alan]

Hi Neil,


> -----Original Message-----
> From: Neil Horman [mailto:nhorman at tuxdriver.com]
> Sent: Monday, September 22, 2014 8:18 PM
> To: Carew, Alan
> Cc: dev at dpdk.org
> Subject: Re: [dpdk-dev] [PATCH 06/10] Alternate implementation of
> librte_power for VM Power Management(Guest).
> 
> On Mon, Sep 22, 2014 at 07:34:35PM +0100, Alan Carew wrote:
> > Re-using the host based librte_power API the alternate implementation uses
> > the guest channel API to forward request for frequency changes to the host
> > monitor.
> > A subset of the librte_power API is supported:
> >  rte_power_init(unsigned lcore_id)
> >  rte_power_exit(unsigned lcore_id)
> >  rte_power_freq_up(unsigned lcore_id)
> >  rte_power_freq_down(unsigned lcore_id)
> >  rte_power_freq_min(unsigned lcore_id)
> >  rte_power_freq_max(unsigned lcore_id)
> >
> > The other unsupported APIs from librte_power return -ENOTSUP.
> >
> > Signed-off-by: Alan Carew <alan.carew at intel.com>
> > ---
> >  lib/librte_power_vm/Makefile    |  49 ++++++++++++++
> >  lib/librte_power_vm/rte_power.c | 146
> ++++++++++++++++++++++++++++++++++++++++
> >  2 files changed, 195 insertions(+)
> >  create mode 100644 lib/librte_power_vm/Makefile
> >  create mode 100644 lib/librte_power_vm/rte_power.c
> >
> NAK.
> This is a bad design choice.  Creating an alternate library with all the same
> symbols in place prevents an application from compiling in support for both host
> and guest power management in parallel (i.e. if an app wants to be able to do
> power management in either environment, and only gets built once, it won't
> work).
> 
> In fact, linking a statically built library with both CONFIG_RTE_LIBRTE_POWER=y
> and CONFIG_RTE_LIBRTE_POWER_VM=y yields the following link-time build
> break:
> 
> LD test
> /home/nhorman/git/dpdk/build/lib/librte_power.a(guest_channel.o): In
> function
> `guest_channel_host_connect':
> guest_channel.c:(.text+0x0): multiple definition of
> `guest_channel_host_connect'
> /home/nhorman/git/dpdk/build/lib/librte_power.a(guest_channel.o):guest_cha
> nnel.c:(.text+0x0):
> first defined here
> /home/nhorman/git/dpdk/build/lib/librte_power.a(guest_channel.o): In
> function
> `guest_channel_send_msg':
> guest_channel.c:(.text+0x370): multiple definition of `guest_channel_send_msg'
> ....
> Ad nauseum.
> 
> What you should do is merge this functionality in with the existing librte power
> library, and make the choice of implementation a run time decision, so theres
> only a single public facing API symbol set, and both implementations can
> coexist, getting chosen at run time (via initialization config option,
> environment detection, etc).  Konstantin and I had a simmilar discussion
> regarding the ACL library and the use of the match function.  I think we came up
> with some reasonably performant solutions.
> 
> Neil

Makes sense, I'll take a look at runtime configuration options and post a V2.

Thanks,
Alan