| Message ID | 20240815214035.1145228-2-mrzhang97@gmail.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | tcp_cubic: fix to achieve at least the same throughput as Reno | expand |
On Thu, Aug 15, 2024 at 5:41 PM Mingrui Zhang <mrzhang97@gmail.com> wrote: > > The original code bypasses bictcp_update() under certain conditions > to reduce the CPU overhead. Intuitively, when last_cwnd==cwnd, > bictcp_update() is executed 32 times per second. As a result, > it is possible that bictcp_update() is not executed for several > RTTs when RTT is short (specifically < 1/32 second = 31 ms and > last_cwnd==cwnd which may happen in small-BDP networks), > thus leading to low throughput in these RTTs. > > The patched code executes bictcp_update() 32 times per second > if RTT > 31 ms or every RTT if RTT < 31 ms, when last_cwnd==cwnd. > > Fixes: df3271f3361b ("[TCP] BIC: CUBIC window growth (2.0)") > Fixes: ac35f562203a ("tcp: bic, cubic: use tcp_jiffies32 instead of tcp_time_stamp") > Signed-off-by: Mingrui Zhang <mrzhang97@gmail.com> > Signed-off-by: Lisong Xu <xu@unl.edu> > --- > v2->v3: Corrent the "Fixes:" footer content > v1->v2: Separate patches > > net/ipv4/tcp_cubic.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c > index 5dbed91c6178..11bad5317a8f 100644 > --- a/net/ipv4/tcp_cubic.c > +++ b/net/ipv4/tcp_cubic.c > @@ -218,8 +218,12 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked) > > ca->ack_cnt += acked; /* count the number of ACKed packets */ > > + /* Update 32 times per second if RTT > 1/32 second, > + * every RTT if RTT < 1/32 second > + * even when last_cwnd == cwnd > + */ > if (ca->last_cwnd == cwnd && > - (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32) > + (s32)(tcp_jiffies32 - ca->last_time) <= min(HZ / 32, usecs_to_jiffies(ca->delay_min))) > return; > > /* The CUBIC function can update ca->cnt at most once per jiffy. > -- I'm getting a compiler error with our builds with clang: net/ipv4/tcp_cubic.c:230:46: error: comparison of distinct pointer types ('typeof (1000 / 32) *' (aka 'int *') and 'typeof (usecs_to_jiffies(ca->delay_min)) *' (aka 'unsigned long *')) [-Werror,-Wcompare-distinct-pointer-types] (s32)(tcp_jiffies32 - ca->last_time) <= min(HZ / 32, usecs_to_jiffies(ca->delay_min))) Can you please try something like the following, which works for our build: (s32)(tcp_jiffies32 - ca->last_time) <= min_t(s32, HZ / 32, usecs_to_jiffies(ca->delay_min))) thanks, neal
On 8/16/24 13:30, Neal Cardwell wrote: > On Thu, Aug 15, 2024 at 5:41 PM Mingrui Zhang <mrzhang97@gmail.com> wrote: >> The original code bypasses bictcp_update() under certain conditions >> to reduce the CPU overhead. Intuitively, when last_cwnd==cwnd, >> bictcp_update() is executed 32 times per second. As a result, >> it is possible that bictcp_update() is not executed for several >> RTTs when RTT is short (specifically < 1/32 second = 31 ms and >> last_cwnd==cwnd which may happen in small-BDP networks), >> thus leading to low throughput in these RTTs. >> >> The patched code executes bictcp_update() 32 times per second >> if RTT > 31 ms or every RTT if RTT < 31 ms, when last_cwnd==cwnd. >> >> Fixes: df3271f3361b ("[TCP] BIC: CUBIC window growth (2.0)") >> Fixes: ac35f562203a ("tcp: bic, cubic: use tcp_jiffies32 instead of tcp_time_stamp") >> Signed-off-by: Mingrui Zhang <mrzhang97@gmail.com> >> Signed-off-by: Lisong Xu <xu@unl.edu> >> --- >> v2->v3: Corrent the "Fixes:" footer content >> v1->v2: Separate patches >> >> net/ipv4/tcp_cubic.c | 6 +++++- >> 1 file changed, 5 insertions(+), 1 deletion(-) >> >> diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c >> index 5dbed91c6178..11bad5317a8f 100644 >> --- a/net/ipv4/tcp_cubic.c >> +++ b/net/ipv4/tcp_cubic.c >> @@ -218,8 +218,12 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked) >> >> ca->ack_cnt += acked; /* count the number of ACKed packets */ >> >> + /* Update 32 times per second if RTT > 1/32 second, >> + * every RTT if RTT < 1/32 second >> + * even when last_cwnd == cwnd >> + */ >> if (ca->last_cwnd == cwnd && >> - (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32) >> + (s32)(tcp_jiffies32 - ca->last_time) <= min(HZ / 32, usecs_to_jiffies(ca->delay_min))) >> return; >> >> /* The CUBIC function can update ca->cnt at most once per jiffy. >> -- > I'm getting a compiler error with our builds with clang: > > net/ipv4/tcp_cubic.c:230:46: error: comparison of distinct pointer > types > ('typeof (1000 / 32) *' (aka 'int *') and > 'typeof (usecs_to_jiffies(ca->delay_min)) *' (aka 'unsigned long *')) > [-Werror,-Wcompare-distinct-pointer-types] > (s32)(tcp_jiffies32 - ca->last_time) <= min(HZ / 32, > usecs_to_jiffies(ca->delay_min))) > > Can you please try something like the following, which works for our build: > > (s32)(tcp_jiffies32 - ca->last_time) <= > min_t(s32, HZ / 32, usecs_to_jiffies(ca->delay_min))) > > thanks, > neal Thank you, Neal, We have tried your suggested changes, and they also work for our compile and experiment tests. Thanks, Mingrui
diff --git a/net/ipv4/tcp_cubic.c b/net/ipv4/tcp_cubic.c index 5dbed91c6178..11bad5317a8f 100644 --- a/net/ipv4/tcp_cubic.c +++ b/net/ipv4/tcp_cubic.c @@ -218,8 +218,12 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd, u32 acked) ca->ack_cnt += acked; /* count the number of ACKed packets */ + /* Update 32 times per second if RTT > 1/32 second, + * every RTT if RTT < 1/32 second + * even when last_cwnd == cwnd + */ if (ca->last_cwnd == cwnd && - (s32)(tcp_jiffies32 - ca->last_time) <= HZ / 32) + (s32)(tcp_jiffies32 - ca->last_time) <= min(HZ / 32, usecs_to_jiffies(ca->delay_min))) return; /* The CUBIC function can update ca->cnt at most once per jiffy.
The original code bypasses bictcp_update() under certain conditions to reduce the CPU overhead. Intuitively, when last_cwnd==cwnd, bictcp_update() is executed 32 times per second. As a result, it is possible that bictcp_update() is not executed for several RTTs when RTT is short (specifically < 1/32 second = 31 ms and last_cwnd==cwnd which may happen in small-BDP networks), thus leading to low throughput in these RTTs. The patched code executes bictcp_update() 32 times per second if RTT > 31 ms or every RTT if RTT < 31 ms, when last_cwnd==cwnd. Fixes: df3271f3361b ("[TCP] BIC: CUBIC window growth (2.0)") Fixes: ac35f562203a ("tcp: bic, cubic: use tcp_jiffies32 instead of tcp_time_stamp") Signed-off-by: Mingrui Zhang <mrzhang97@gmail.com> Signed-off-by: Lisong Xu <xu@unl.edu> --- v2->v3: Corrent the "Fixes:" footer content v1->v2: Separate patches net/ipv4/tcp_cubic.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)