Re: [PATCH] time/timecounter: inline timecounter_cyc2time()

[Kevin Yang]

Reviewed-by: Kevin Yang <yyd@xxxxxxxxxx>


On Sat, Nov 29, 2025 at 12:06 PM Willem de Bruijn
<willemdebruijn.kernel@xxxxxxxxx> wrote:
>
> Eric Dumazet wrote:
> > New network transport protocols want NIC drivers to get hwtstamps
> > of all incoming packets, and possibly all outgoing packets.
> >
> > Swift congestion control is used by good old TCP transport and is
> > our primary need for timecounter_cyc2time(). This will be upstreamed soon.
> >
> > This means timecounter_cyc2time() can be called more than 100 million
> > times per second on a busy server.
> >
> > Inlining timecounter_cyc2time() brings a 12 % improvement on a
> > UDP receive stress test on a 100Gbit NIC.
> >
> > Note that FDO, LTO, PGO are unable to magically help for this
> > case, presumably because NIC drivers are almost exclusively shipped
> > as modules.
> >
> > Add an unlikely() around the cc_cyc2ns_backwards() case,
> > even if FDO (when used) is able to take care of this optimization.
> >
> > Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
> > Link: https://research.google/pubs/swift-delay-is-simple-and-effective-for-congestion-control-in-the-datacenter/
> > Cc: Kevin Yang <yyd@xxxxxxxxxx>
> > Cc: Willem de Bruijn <willemb@xxxxxxxxxx>
> > Cc: Neal Cardwell <ncardwell@xxxxxxxxxx>
> > Cc: Yuchung Cheng <ycheng@xxxxxxxxxx>
>
> Reviewed-by: Willem de Bruijn <willemb@xxxxxxxxxx>