-----Original Message-----
> Date: Wed, 11 Oct 2017 21:25:58 +0200
> From: Thomas Monjalon <tho...@monjalon.net>
> To: Jerin Jacob <jerin.ja...@caviumnetworks.com>
> Cc: Gowrishankar <gowrishanka...@linux.vnet.ibm.com>, dev@dpdk.org, Chao
> Zhu <chao...@linux.vnet.ibm.com>, Bruce Richardson
> <bruce.richard...@intel.com>, Konstantin Ananyev
> <konstantin.anan...@intel.com>, vikto...@rehivetech.com,
> jianbo....@linaro.org
> Subject: Re: [dpdk-dev] [PATCH v2 5/5] eal/timer: honor architecture
> specific rdtsc hz function
>
> 11/10/2017 20:57, Jerin Jacob:
> > From: Thomas Monjalon <tho...@monjalon.net>
> > > 22/09/2017 10:25, Gowrishankar:
> > > > From: Jerin Jacob <jerin.ja...@caviumnetworks.com>
> > > >
> > > > When calibrating the tsc frequency, first, probe the architecture
> > > > specific
> > > > rdtsc hz function. if not available, use the existing calibrate scheme
> > > > to calibrate the tsc frequency.
> > > >
> > > > Signed-off-by: Jerin Jacob <jerin.ja...@caviumnetworks.com>
> > >
> > > I agree on the idea.
> >
> > OK
> >
> > > The namespace of cycles related function in DPDK is a real mess.
> >
> > Absolutely!!
> >
> > > I think we can choose better names in this series as a first step
> > > to tidy this mess.
> > > I will explain below.
> > >
> > > At first, we should avoid TSC and RDTSC which are Intel-only wording.
> > > The generic word could be "cycles" (the word used in arch headers),
> > > or "ticks".
> > > We should also name the timer sources or their function in a generic way.
> > > Examples: CPU cycles? fast counter? precise counter?
> > >
> > > Sometimes we use "hz", sometimes "freq".
> > > It would better to keep one of them.
> > >
> > > > --- a/lib/librte_eal/common/eal_common_timer.c
> > > > +++ b/lib/librte_eal/common/eal_common_timer.c
> > > > @@ -80,8 +80,11 @@
> > > > void
> > > > set_tsc_freq(void)
> > > > {
> > > > - uint64_t freq = get_tsc_freq();
> > > > + uint64_t freq;
> > > >
> > > > + freq = rte_rdtsc_arch_hz();
> > >
> > > This new function is arch-specific and exported as a new API.
> >
> > I thought of avoid exporting it. But then if the function is in
> > lib/librte_eal/common/include/arch/../rte_cycles.h it is anyway exposed to
> > application. i.e whatever files in lib/librte_eal/common/include/arch/../
> > anyway exposed to application.
>
> Ah yes, you are right!
>
> > See last comment.
> >
> > >
> > > > + if (!freq)
> > > > + freq = get_tsc_freq();
> > >
> > > The function get_tsc_freq is guessing the freq with OS-specific method.
> > >
> > > > if (!freq)
> > > > freq = estimate_tsc_freq();
> > >
> > > The function estimate_tsc_freq is doing an estimation based on sleep().
> > >
> > > At the end, the most accurate frequency is saved in eal_tsc_resolution_hz
> > > and can be retrieved with rte_get_tsc_hz().
> > > I don't understand why rte_rdtsc_arch_hz() is also exported to the apps.
> > >
> > > TSC and HPET timer sources are wrapped in rte_get_timer_hz() in the
> > > Similarly we can get the current timer with rte_get_timer_cycles().
> > > In the case of TSC, it calls rte_get_tsc_cycles() which is an alias
> > > of rte_rdtsc().
> > > Some code is still using directly rte_rdtsc().
> > > There is also rte_rdtsc_precise which adds a memory barrier.
> > >
> > > The real question is what is the right abstraction for the application?
> > > Do we want the fastest timer? the CPU timer? a precise timer?
> > >
> > > I would like to see a real discussion on this topic, in order of building
> > > a new timer API which would alias the old one for some time.
> >
> > I guess, we may need to see to how abstract vmware TSC support also in
> > proper way
>
> Yes
>
> > > If you don't want to bother with all these questions, I suggest to not
> > > export the new function rte_rdtsc_arch_hz() and rename it to tsc_arch_hz.
> >
> > If I understand it correctly, You would like to create a header file
> > in lib/librte_eal/common/include/arch/../ which should not be exported and
> > change
> > the name to tsc_arch_hz.
>
> I had not think about the way to do this.
> What about having internal headers in lib/librte_eal/common/arch/ ?
Looks bit odd when compare with existing scheme of arch function management.
Anyway the whole timer stuff needs to be cleanup.
I think, we can take that when do the cleanup.
On the other side, This API has real ARM64, PPC, x86 implementation now.
I think,it is important to have this feature for v17.11
>
