[dpdk-dev] [PATCH v3] Patch introducing API to read/write Intel Architecture Model Specific Registers (MSR)...

[Andralojc, WojciechX]

> -----Original Message-----
> From: Ananyev, Konstantin
> Sent: Friday, January 22, 2016 11:05 AM
> To: Panu Matilainen; Andralojc, WojciechX
> Cc: dev at dpdk.org
> Subject: RE: [dpdk-dev] [PATCH v3] Patch introducing API to read/write Intel
> Architecture Model Specific Registers (MSR)...
> 
> > -----Original Message-----
> > From: Panu Matilainen [mailto:pmatilai at redhat.com]
> > Sent: Friday, January 22, 2016 10:06 AM
> > To: Ananyev, Konstantin; Andralojc, WojciechX
> > Cc: dev at dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH v3] Patch introducing API to read/write Intel
> Architecture Model Specific Registers (MSR)...
> >
> > On 01/21/2016 12:51 PM, Ananyev, Konstantin wrote:
> > > Hi Panu,
> > >
> > >> -----Original Message-----
> > >> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Panu
> > >> Matilainen
> > >> Sent: Thursday, January 21, 2016 10:39 AM
> > >> To: Andralojc, WojciechX
> > >> Cc: dev at dpdk.org
> > >> Subject: Re: [dpdk-dev] [PATCH v3] Patch introducing API to read/write
> Intel Architecture Model Specific Registers (MSR)...
> > >>
> > >> On 01/21/2016 10:18 AM, Wojciech Andralojc wrote:
> > >>> Patch reworked.
> > >>>
> > >>> Signed-off-by: Wojciech Andralojc <wojciechx.andralojc at intel.com>
> > >>> ---
> > >>>    lib/librte_eal/common/include/arch/x86/rte_msr.h |  88
> +++++++++++++++++
> > >>>    lib/librte_eal/linuxapp/eal/Makefile             |   1 +
> > >>>    lib/librte_eal/linuxapp/eal/arch/x86/rte_msr.c   | 116
> +++++++++++++++++++++++
> > >>>    3 files changed, 205 insertions(+)
> > >>>    create mode 100644
> lib/librte_eal/common/include/arch/x86/rte_msr.h
> > >>>    create mode 100644
> > >>> lib/librte_eal/linuxapp/eal/arch/x86/rte_msr.c
> > >>
> > >> This creates a new arch-specific public API, with rte_msr.h
> > >> installed as a public header and implementation in the library (as
> > >> opposed to inline), and so the new functions would have to be added
> > >> to rte_eal_version.map.
> > >>
> > >> However that is a bit of a problem since it only exists on IA
> > >> architectures, so it'd mean dummy entries in the version map for
> > >> all other architectures. All the other arch-specific APIs are
> > >> inline code so this is the first of its kind.
> > >
> > > My thought was:
> > > 1. implementation is linux specific (as I know not supposed to work under
> freebsd).
> > > 2. they are not supposed to be used at run-time cide-path, so no need to be
> inlined.
> >
> > Speed is not the only interesting attribute of inlining, inlined code
> > also effectively escapes the library ABI so it does not need
> > versioning / exporting.
> >
> > > 3. As I understand we plan to  have a library that will use these functions
> anyway.
> >
> > Is this library going to be a generic or specific to Intel CPUs?
> 
> As I understand - yes.
> It supposed to utilise new Intel chips CAT abilities.
> Wojciech, please correct me if I missed something here.

Konstantin, yes, you are right,
CAT enabling lib is Intel CPUs specific.

> 
> > Also, if there are no other uses for the MSR API at the moment,
> > perhaps the best place for this code would be within that library anyway?
> 
> Sounds good to me.

OK, sounds good.
Thank you both for your input.

> 
> Konstantin
> 
> >
> > > About dummy entries in the .map file: if we'll create a 'weak'
> > > generic implementation, that would just return an error - would it solve the
> issue?
> >
> > Sure it'd solve the issue of dummy entries in .map but people seemed
> > opposed to having a highly arch-specific API exposed to all architectures.
> >
> > 	- Panu -
> >

Wojciech Andralojc