netdev - Re: [PATCH iproute2-next 1/3] tc: support conversions to or from 64 bit nanosecond-based time

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Date:   Mon, 13 Aug 2018 11:37:48 -0700
From:   Dave Taht <dave.taht@...il.com>
To:     David Ahern <dsahern@...il.com>
Cc:     Yousuk Seung <ysseung@...gle.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Michael McLennan <nefario@...gle.com>,
        Priyaranjan Jha <priyarjha@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH iproute2-next 1/3] tc: support conversions to or from 64
 bit nanosecond-based time

On Sun, Aug 12, 2018 at 3:09 PM David Ahern <dsahern@...il.com> wrote:
>
> On 8/6/18 11:09 AM, Yousuk Seung wrote:
> > diff --git a/tc/tc_core.h b/tc/tc_core.h
> > index 1dfa9a4f773b..a0fe0923d171 100644
> > --- a/tc/tc_core.h
> > +++ b/tc/tc_core.h
> > @@ -7,6 +7,10 @@
> >
> >  #define TIME_UNITS_PER_SEC   1000000
> >
> > +#define NSEC_PER_USEC 1000
> > +#define NSEC_PER_MSEC 1000000
> > +#define NSEC_PER_SEC 1000000000LL
> > +
>
> These are not specific to tc so a header in include is a better location
> (utils.h or a new one)
>
> >  enum link_layer {
> >       LINKLAYER_UNSPEC,
> >       LINKLAYER_ETHERNET,
> > diff --git a/tc/tc_util.c b/tc/tc_util.c
> > index d7578528a31b..c39c9046dcae 100644
> > --- a/tc/tc_util.c
> > +++ b/tc/tc_util.c
>
> Similarly for these time functions - not specific to tc so move to
> lib/utils.c
>
> > @@ -385,6 +385,61 @@ char *sprint_ticks(__u32 ticks, char *buf)
> >       return sprint_time(tc_core_tick2time(ticks), buf);
> >  }
> >
> > +/* 64 bit times are represented internally in nanoseconds */
> > +int get_time64(__s64 *time, const char *str)
>
> __u64 seems more appropriate than __s64

The reason why these are signed is to leave room in the API to
print/manage negative values. Wasting the 64th bit thusly would only
matter after extreme uptimes.

There was something of a long debate on this when these patches went
around the first time. We ended up with signed time in the netem code
also.


> > +{
> > +     double nsec;
> > +     char *p;
> > +
> > +     nsec = strtod(str, &p);
> > +     if (p == str)
> > +             return -1;
> > +
> > +     if (*p) {
> > +             if (strcasecmp(p, "s") == 0 ||
> > +                 strcasecmp(p, "sec") == 0 ||
> > +                 strcasecmp(p, "secs") == 0)
> > +                     nsec *= NSEC_PER_SEC;
> > +             else if (strcasecmp(p, "ms") == 0 ||
> > +                      strcasecmp(p, "msec") == 0 ||
> > +                      strcasecmp(p, "msecs") == 0)
> > +                     nsec *= NSEC_PER_MSEC;
> > +             else if (strcasecmp(p, "us") == 0 ||
> > +                      strcasecmp(p, "usec") == 0 ||
> > +                      strcasecmp(p, "usecs") == 0)
> > +                     nsec *= NSEC_PER_USEC;
> > +             else if (strcasecmp(p, "ns") == 0 ||
> > +                      strcasecmp(p, "nsec") == 0 ||
> > +                      strcasecmp(p, "nsecs") == 0)
>
> strncasecmp would be more efficient
>
> > +                     nsec *= 1;
> > +             else
> > +                     return -1;
> > +     }
> > +
> > +     *time = nsec;
> > +     return 0;
> > +}
> > +
> > +void print_time64(char *buf, int len, __s64 time)
> > +{
> > +     double nsec = time;
> > +
> > +     if (time >= NSEC_PER_SEC)
> > +             snprintf(buf, len, "%.3fs", nsec/NSEC_PER_SEC);
> > +     else if (time >= NSEC_PER_MSEC)
> > +             snprintf(buf, len, "%.3fms", nsec/NSEC_PER_MSEC);
> > +     else if (time >= NSEC_PER_USEC)
> > +             snprintf(buf, len, "%.3fus", nsec/NSEC_PER_USEC);
> > +     else
> > +             snprintf(buf, len, "%lldns", time);
> > +}
> > +
> > +char *sprint_time64(__s64 time, char *buf)
> > +{
> > +     print_time64(buf, SPRINT_BSIZE-1, time);
> > +     return buf;
> > +}
> > +
> >  int get_size(unsigned int *size, const char *str)
> >  {
> >       double sz;



-- 

Dave Täht
CEO, TekLibre, LLC
http://www.teklibre.com
Tel: 1-669-226-2619