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tcp: Refactor tcp_get_srtt()

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Refactor tcp_get_srtt() into its two component operations: unit
conversion and shifting. No functional change is intended.

Reviewed by:	cc, tuexen
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D40304
This commit is contained in:
Jonathan T. Looney 2023-05-31 19:16:20 +00:00
parent eb2b00da56
commit 4f2cc73f34
1 changed files with 27 additions and 22 deletions
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49
sys/netinet/tcp_subr.c
View file

@ -4647,28 +4647,33 @@ tcp_get_srtt(struct tcpcb *tp, int granularity)
{
uint32_t srtt;
if (tp->t_tmr_granularity == TCP_TMR_GRANULARITY_USEC)
srtt = tp->t_srtt;
else if (tp->t_tmr_granularity == TCP_TMR_GRANULARITY_TICKS) {
/* TICKS are stored shifted; unshift for the real TICKS */
srtt = tp->t_srtt >> TCP_RTT_SHIFT;
}
if (tp->t_tmr_granularity == granularity)
return (srtt);
/* If we reach here they are oppsite what the caller wants */
if (granularity == TCP_TMR_GRANULARITY_USEC) {
/*
* The user wants useconds and internally
* its kept in ticks, convert to useconds.
* Put unshift at last improves precision.
*/
srtt = TICKS_2_USEC(tp->t_srtt) >> TCP_RTT_SHIFT;
} else if (granularity == TCP_TMR_GRANULARITY_TICKS) {
/*
* The user wants ticks and internally its
* kept in useconds, convert to ticks.
*/
srtt = USEC_2_TICKS(srtt);
KASSERT(granularity == TCP_TMR_GRANULARITY_USEC ||
granularity == TCP_TMR_GRANULARITY_TICKS,
("%s: called with unexpected granularity %d", __func__,
granularity));
srtt = tp->t_srtt;
/*
* We only support two granularities. If the stored granularity
* does not match the granularity requested by the caller,
* convert the stored value to the requested unit of granularity.
*/
if (tp->t_tmr_granularity != granularity) {
if (granularity == TCP_TMR_GRANULARITY_USEC)
srtt = TICKS_2_USEC(srtt);
else
srtt = USEC_2_TICKS(srtt);
}
/*
* If the srtt is stored with ticks granularity, we need to
* unshift to get the actual value. We do this after the
* conversion above (if one was necessary) in order to maximize
* precision.
*/
if (tp->t_tmr_granularity == TCP_TMR_GRANULARITY_TICKS)
srtt = srtt >> TCP_RTT_SHIFT;
return (srtt);
}