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author | David S. Miller <davem@davemloft.net> | 2014-10-03 12:37:23 -0700 |
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committer | David S. Miller <davem@davemloft.net> | 2014-10-03 12:37:23 -0700 |
commit | c2bf5ec20488fb91af32f1c7f7c63f338ebacc9f (patch) | |
tree | ee3dc48d33d56e11df19b52c33abf2ac85667079 /net | |
parent | 38df6492eb511d2a6823303cb1a194c4fe423154 (diff) | |
parent | 808e7ac0bdef31204184904f6b3ea356a30a9ed5 (diff) |
Merge branch 'qdisc_bulk_dequeue'
Jesper Dangaard Brouer says:
====================
qdisc: bulk dequeue support
This patchset uses DaveM's recent API changes to dev_hard_start_xmit(),
from the qdisc layer, to implement dequeue bulking.
Patch01: "qdisc: bulk dequeue support for qdiscs with TCQ_F_ONETXQUEUE"
- Implement basic qdisc dequeue bulking
- This time, 100% relying on BQL limits, no magic safe-guard constants
Patch02: "qdisc: dequeue bulking also pickup GSO/TSO packets"
- Extend bulking to bulk several GSO/TSO packets
- Seperate patch, as it introduce a small regression, see test section.
We do have a patch03, which exports a userspace tunable as a BQL
tunable, that can byte-cap or disable the bulking/bursting. But we
could not agree on it internally, thus not sending it now. We
basically strive to avoid adding any new userspace tunable.
Testing patch01:
================
Demonstrating the performance improvement of qdisc dequeue bulking, is
tricky because the effect only "kicks-in" once the qdisc system have a
backlog. Thus, for a backlog to form, we need either 1) to exceed wirespeed
of the link or 2) exceed the capability of the device driver.
For practical use-cases, the measureable effect of this will be a
reduction in CPU usage
01-TCP_STREAM:
--------------
Testing effect for TCP involves disabling TSO and GSO, because TCP
already benefit from bulking, via TSO and especially for GSO segmented
packets. This patch view TSO/GSO as a seperate kind of bulking, and
avoid further bulking of these packet types.
The measured perf diff benefit (at 10Gbit/s) for a single netperf
TCP_STREAM were 9.24% less CPU used on calls to _raw_spin_lock()
(mostly from sch_direct_xmit).
If my E5-2695v2(ES) CPU is tuned according to:
http://netoptimizer.blogspot.dk/2014/04/basic-tuning-for-network-overload.html
Then it is possible that a single netperf TCP_STREAM, with GSO and TSO
disabled, can utilize all bandwidth on a 10Gbit/s link. This will
then cause a standing backlog queue at the qdisc layer.
Trying to pressure the system some more CPU util wise, I'm starting
24x TCP_STREAMs and monitoring the overall CPU utilization. This
confirms bulking saves CPU cycles when it "kicks-in".
Tool mpstat, while stressing the system with netperf 24x TCP_STREAM, shows:
* Disabled bulking: sys:2.58% soft:8.50% idle:88.78%
* Enabled bulking: sys:2.43% soft:7.66% idle:89.79%
02-UDP_STREAM
-------------
The measured perf diff benefit for UDP_STREAM were 6.41% less CPU used
on calls to _raw_spin_lock(). 24x UDP_STREAM with packet size -m 1472 (to
avoid sending UDP/IP fragments).
03-trafgen driver test
----------------------
The performance of the 10Gbit/s ixgbe driver is limited due to
updating the HW ring-queue tail-pointer on every packet. As
previously demonstrated with pktgen.
Using trafgen to send RAW frames from userspace (via AF_PACKET), and
forcing it through qdisc path (with option --qdisc-path and -t0),
sending with 12 CPUs.
I can demonstrate this driver layer limitation:
* 12.8 Mpps with no qdisc bulking
* 14.8 Mpps with qdisc bulking (full 10G-wirespeed)
Testing patch02:
================
Testing Bulking several GSO/TSO packets:
Measuring HoL (Head-of-Line) blocking for TSO and GSO, with
netperf-wrapper. Bulking several TSO show no performance regressions
(requeues were in the area 32 requeues/sec for 10G while transmitting
approx 813Kpps).
Bulking several GSOs does show small regression or very small
improvement (requeues were in the area 8000 requeues/sec, for 10G
while transmitting approx 813Kpps).
Using ixgbe 10Gbit/s with GSO bulking, we can measure some additional
latency. Base-case, which is "normal" GSO bulking, sees varying
high-prio queue delay between 0.38ms to 0.47ms. Bulking several GSOs
together, result in a stable high-prio queue delay of 0.50ms.
Corrosponding to:
(10000*10^6)*((0.50-0.47)/10^3)/8 = 37500 bytes
(10000*10^6)*((0.50-0.38)/10^3)/8 = 150000 bytes
37500/1500 = 25 pkts
150000/1500 = 100 pkts
Using igb at 100Mbit/s with GSO bulking, shows an improvement.
Base-case sees varying high-prio queue delay between 2.23ms to 2.35ms
diff of 0.12ms corrosponding to 1500 bytes at 100Mbit/s. Bulking
several GSOs together, result in a stable high-prio queue delay of
2.23ms.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r-- | net/sched/sch_generic.c | 40 |
1 files changed, 38 insertions, 2 deletions
diff --git a/net/sched/sch_generic.c b/net/sched/sch_generic.c index 7c8e5d73d433..797ebef73642 100644 --- a/net/sched/sch_generic.c +++ b/net/sched/sch_generic.c @@ -56,6 +56,35 @@ static inline int dev_requeue_skb(struct sk_buff *skb, struct Qdisc *q) return 0; } +static struct sk_buff *try_bulk_dequeue_skb(struct Qdisc *q, + struct sk_buff *head_skb, + int bytelimit) +{ + struct sk_buff *skb, *tail_skb = head_skb; + + while (bytelimit > 0) { + skb = q->dequeue(q); + if (!skb) + break; + + bytelimit -= skb->len; /* covers GSO len */ + skb = validate_xmit_skb(skb, qdisc_dev(q)); + if (!skb) + break; + + while (tail_skb->next) /* GSO list goto tail */ + tail_skb = tail_skb->next; + + tail_skb->next = skb; + tail_skb = skb; + } + + return head_skb; +} + +/* Note that dequeue_skb can possibly return a SKB list (via skb->next). + * A requeued skb (via q->gso_skb) can also be a SKB list. + */ static inline struct sk_buff *dequeue_skb(struct Qdisc *q) { struct sk_buff *skb = q->gso_skb; @@ -70,10 +99,17 @@ static inline struct sk_buff *dequeue_skb(struct Qdisc *q) } else skb = NULL; } else { - if (!(q->flags & TCQ_F_ONETXQUEUE) || !netif_xmit_frozen_or_stopped(txq)) { + if (!(q->flags & TCQ_F_ONETXQUEUE) || + !netif_xmit_frozen_or_stopped(txq)) { + int bytelimit = qdisc_avail_bulklimit(txq); + skb = q->dequeue(q); - if (skb) + if (skb) { + bytelimit -= skb->len; skb = validate_xmit_skb(skb, qdisc_dev(q)); + } + if (skb && qdisc_may_bulk(q)) + skb = try_bulk_dequeue_skb(q, skb, bytelimit); } } |