Re: [PATCH net-next 1/2] net: remove NET_LL_RX_POLL config menue

[Daniel Borkmann]

On 06/13/2013 04:13 AM, Eliezer Tamir wrote:
> On 13/06/2013 05:01, Stephen Hemminger wrote:
> > On Wed, 12 Jun 2013 15:12:05 -0700 (PDT)
> > David Miller <davem@xxxxxxxxxxxxx> wrote:
> >
> > > From: Eliezer Tamir <eliezer.tamir@xxxxxxxxxxxxxxx>
> > > Date: Tue, 11 Jun 2013 17:24:28 +0300
> > >
> > > >       depends on X86_TSC
> > >
> > > Wait a second, I didn't notice this before.  There needs to be a better
> > > way to test for the accuracy you need, or if the issue is lack of a proper
> > > API for cycle counter reading, fix that rather than add ugly arch
> > > specific dependencies to generic networking code.
> >
> > This should be sched_clock(), rather than direct TSC access.
> > Also any code using TSC or sched_clock has to be carefully audited to deal with
> > clocks running at different rates on different CPU's. Basically value is only
> > meaning full on same CPU.
>
> OK,
>
> If we covert to sched_clock(), would adding a define such as HAVE_HIGH_PRECISION_CLOCK to architectures that have both a high precision clock and a 64 bit cycles_t be a good solution?
>
> (if not any other suggestion?)

Hm, probably cpu_clock() and similar might be better, since they use
sched_clock() in the background when !CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
(meaning when sched_clock() provides synchronized highres time source from
the architecture), and, quoting ....

 Otherwise it tries to create a semi stable clock from a mixture of other
 clocks, including:

  - GTOD (clock monotomic)
  - sched_clock()
  - explicit idle events

But yeah, it needs to be evaluated regarding the drift between CPUs in
general.

Then, eventually, you could get rid of the entire NET_LL_RX_POLL config
option plus related ifdefs in the code and have it built-in in general?
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