From: Thomas Monjalon <thomas@monjalon.net>
To: Alan Dewar <alan.dewar@att.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
"alangordondewar@gmail.com" <alangordondewar@gmail.com>,
"Dumitrescu, Cristian" <cristian.dumitrescu@intel.com>,
"Singh, Jasvinder" <jasvinder.singh@intel.com>
Subject: Re: [dpdk-dev] [PATCH v2] sched: fix port time rounding error
Date: Tue, 07 Jul 2020 01:01:17 +0200 [thread overview]
Message-ID: <1904548.GDZOGqOs03@thomas> (raw)
In-Reply-To: <CY4PR11MB0072C105F5E0AFEA0F8BFC5AE0690@CY4PR11MB0072.namprd11.prod.outlook.com>
> > 25/06/2020 11:59, alangordondewar@gmail.com:
> > > From: Alan Dewar <alan.dewar@att.com>
> > >
> > > The QoS scheduler works off port time that is computed from the number
> > > of CPU cycles that have elapsed since the last time the port was
> > > polled. It divides the number of elapsed cycles to calculate how
> > > many bytes can be sent, however this division can generate rounding
> > > errors, where some fraction of a byte sent may be lost.
> > >
> > > Lose enough of these fractional bytes and the QoS scheduler
> > > underperforms. The problem is worse with low bandwidths.
> > >
> > > To compensate for this rounding error this fix doesn't advance the
> > > port's time_cpu_cycles by the number of cycles that have elapsed, but
> > > by multiplying the computed number of bytes that can be sent (which
> > > has been rounded down) by number of cycles per byte.
> > > This will mean that port's time_cpu_cycles will lag behind the CPU
> > > cycles momentarily. At the next poll, the lag will be taken into
> > > account.
> > >
> > > v2:
> > > If the cycles value wraps (100 year+) reset the port's cpu cycle back
> > > to zero.
> > >
> > > Fixes: de3cfa2c98 ("sched: initial import")
> > >
> > > Signed-off-by: Alan Dewar <alan.dewar@att.com>
>
> Acked-by: Jasvinder Singh <jasvinder.singh@intel.com>
Applied, thanks
next prev parent reply other threads:[~2020-07-06 23:01 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-16 8:48 [dpdk-dev] [PATCH] " alangordondewar
2020-04-17 21:19 ` Dumitrescu, Cristian
2020-04-20 11:23 ` Singh, Jasvinder
2020-04-21 8:21 ` Dewar, Alan
2020-06-24 22:50 ` Thomas Monjalon
2020-06-25 8:32 ` Singh, Jasvinder
2020-06-25 8:40 ` Alan Dewar
2020-06-25 9:59 ` [dpdk-dev] [PATCH v2] " alangordondewar
2020-07-05 20:41 ` Thomas Monjalon
2020-07-06 21:20 ` Singh, Jasvinder
2020-07-06 23:01 ` Thomas Monjalon [this message]
2020-08-20 14:32 ` Kevin Traynor
2020-08-21 15:28 ` Kinsella, Ray
2020-09-07 10:09 ` Kevin Traynor
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