The branch main has been updated by jtl:
URL:
https://cgit.FreeBSD.org/src/commit/?id=4f2cc73f34eb5f4bd6e66afda1c367676547f516
commit 4f2cc73f34eb5f4bd6e66afda1c367676547f516
Author: Jonathan T. Looney <j...@freebsd.org>
AuthorDate: 2023-05-31 19:16:20 +0000
Commit: Jonathan T. Looney <j...@freebsd.org>
CommitDate: 2023-05-31 19:16:20 +0000
tcp: Refactor tcp_get_srtt()
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
---
sys/netinet/tcp_subr.c | 49 +++++++++++++++++++++++++++----------------------
1 file changed, 27 insertions(+), 22 deletions(-)
diff --git a/sys/netinet/tcp_subr.c b/sys/netinet/tcp_subr.c
index 52222d7c1634..fe065fd08737 100644
--- a/sys/netinet/tcp_subr.c
+++ b/sys/netinet/tcp_subr.c
@@ -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);
}
