Re: [dpdk-dev] [PATCH v2 RESEND] timer: remove check_tsc_flags()

[Stephen Hemminger <stephen@networkplumber.org>]

On Tue, 8 Oct 2019 09:36:49 +0100
Bruce Richardson <bruce.richardson@intel.com> wrote:

> On Mon, Oct 07, 2019 at 04:18:54PM -0700, Stephen Hemminger wrote:
> > On Mon, 07 Oct 2019 08:40:05 -0700 Jim Harris <james.r.harris@intel.com>
> > wrote:
> >   
> > > This code was added 7+ years ago:
> > > 
> > > commit fb022b85bae4 ("timer: check TSC reliability")
> > > 
> > > presumably when variant TSCs were still somewhat common?  But this code
> > > doesn't do anything except print a warning, and the warning doesn't
> > > give any kind of advice to the user, so let's just remove it.
> > > 
> > > While the warning has no functional meaning, the /proc/cpuinfo parsing
> > > consumes a non-trivial amount of time which is especially noticeable in
> > > secondary processes.  On my test system, it consumes 21ms out of the
> > > 66ms total execution time for rte_eal_init() in a secondary process.
> > > 
> > > Signed-off-by: Jim Harris <james.r.harris@intel.com>  
> > 
> > Yes this code is dead.
> > 
> > Acked-by: Stephen Hemminger <stephen@networkplumber.org>
> >   
> 
> +1 for this. Even if it was needed, we should never parse /proc/cpuinfo,
> since we have a DPDK function to query cpuid directly anyway.
> 
> Acked-by: Bruce Richardson <bruce.richardson@intel.com>

It also turns out that Hyper-V/Azure report unstable TSC because
when VM is migrated there are blips in TSC. There upcoming changes to
handle that in Hypervisor and Linux drivers.