Hi Cong,
On Fri, Jan 29, 2021 at 03:04:51PM -0800, Cong Wang wrote:
> On Fri, Jan 29, 2021 at 2:29 AM Simon Horman <simon.hor...@netronome.com>
> wrote:
> > +/**
> > + * psched_ratecfg_precompute__() - Pre-compute values for reciprocal
> > division
> > + * @rate: Rate to compute reciprocal division values of
> > + * @mult: Multiplier for reciprocal division
> > + * @shift: Shift for reciprocal division
> > + *
> > + * The multiplier and shift for reciprocal division by rate are stored
> > + * in mult and shift.
> > + *
> > + * The deal here is to replace a divide by a reciprocal one
> > + * in fast path (a reciprocal divide is a multiply and a shift)
> > + *
> > + * Normal formula would be :
> > + * time_in_ns = (NSEC_PER_SEC * len) / rate_bps
> > + *
> > + * We compute mult/shift to use instead :
> > + * time_in_ns = (len * mult) >> shift;
> > + *
> > + * We try to get the highest possible mult value for accuracy,
> > + * but have to make sure no overflows will ever happen.
> > + *
> > + * reciprocal_value() is not used here it doesn't handle 64-bit values.
> > + */
> > +static void psched_ratecfg_precompute__(u64 rate, u32 *mult, u8 *shift)
>
> Am I the only one who thinks "foo__()" is an odd name? We usually use
> "__foo()" for helper or unlocked version of "foo()".
Sorry, I will fix that.
> And, you probably want to move the function doc to its exported variant
> instead, right?
Would something like this incremental change your concerns?
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c
index 44991ea726fc..63cb69df4240 100644
--- a/net/sched/sch_generic.c
+++ b/net/sched/sch_generic.c
@@ -1325,14 +1325,7 @@ void dev_shutdown(struct net_device *dev)
WARN_ON(timer_pending(&dev->watchdog_timer));
}
-/**
- * psched_ratecfg_precompute__() - Pre-compute values for reciprocal division
- * @rate: Rate to compute reciprocal division values of
- * @mult: Multiplier for reciprocal division
- * @shift: Shift for reciprocal division
- *
- * The multiplier and shift for reciprocal division by rate are stored
- * in mult and shift.
+/* Pre-compute values for reciprocol division for a rate limit.
*
* The deal here is to replace a divide by a reciprocal one
* in fast path (a reciprocal divide is a multiply and a shift)
@@ -1348,7 +1341,7 @@ void dev_shutdown(struct net_device *dev)
*
* reciprocal_value() is not used here it doesn't handle 64-bit values.
*/
-static void psched_ratecfg_precompute__(u64 rate, u32 *mult, u8 *shift)
+static void __psched_ratecfg_precompute(u64 rate, u32 *mult, u8 *shift)
{
u64 factor = NSEC_PER_SEC;
@@ -1367,6 +1360,15 @@ static void psched_ratecfg_precompute__(u64 rate, u32
*mult, u8 *shift)
}
}
+/**
+ * psched_ratecfg_precompute() - Pre-compute values for byte rate limiting
+ * @r: Byte-per-second rate struct to store configuration in
+ * @conf: Rate specification
+ * @rate64: Rate in bytes-per-second
+ *
+ * Pre-compute configuration, including values for reciprocal division,
+ * for a byte-per-second rate limit.
+ */
void psched_ratecfg_precompute(struct psched_ratecfg *r,
const struct tc_ratespec *conf,
u64 rate64)
@@ -1375,14 +1377,22 @@ void psched_ratecfg_precompute(struct psched_ratecfg *r,
r->overhead = conf->overhead;
r->rate_bytes_ps = max_t(u64, conf->rate, rate64);
r->linklayer = (conf->linklayer & TC_LINKLAYER_MASK);
- psched_ratecfg_precompute__(r->rate_bytes_ps, &r->mult, &r->shift);
+ __psched_ratecfg_precompute(r->rate_bytes_ps, &r->mult, &r->shift);
}
EXPORT_SYMBOL(psched_ratecfg_precompute);
+/**
+ * psched_ppscfg_precompute() - Pre-compute values for packet rate limiting
+ * @r: Packet-per-second rate struct to store configuration in
+ * @pktrate64: Rate in packets-per-second
+ *
+ * Pre-compute configuration, including values for reciprocal division,
+ * for a packet-per-second rate limit.
+ */
void psched_ppscfg_precompute(struct psched_pktrate *r, u64 pktrate64)
{
r->rate_pkts_ps = pktrate64;
- psched_ratecfg_precompute__(r->rate_pkts_ps, &r->mult, &r->shift);
+ __psched_ratecfg_precompute(r->rate_pkts_ps, &r->mult, &r->shift);
}
EXPORT_SYMBOL(psched_ppscfg_precompute);
