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edb09eb17e
Large tc dumps (tc -s {qdisc|class} sh dev ethX) done by Google BwE host
agent [1] are problematic at scale :
For each qdisc/class found in the dump, we currently lock the root qdisc
spinlock in order to get stats. Sampling stats every 5 seconds from
thousands of HTB classes is a challenge when the root qdisc spinlock is
under high pressure. Not only the dumps take time, they also slow
down the fast path (queue/dequeue packets) by 10 % to 20 % in some cases.
An audit of existing qdiscs showed that sch_fq_codel is the only qdisc
that might need the qdisc lock in fq_codel_dump_stats() and
fq_codel_dump_class_stats()
In v2 of this patch, I now use the Qdisc running seqcount to provide
consistent reads of packets/bytes counters, regardless of 32/64 bit arches.
I also changed rate estimators to use the same infrastructure
so that they no longer need to lock root qdisc lock.
[1]
http://static.googleusercontent.com/media/research.google.com/en//pubs/archive/43838.pdf
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Cong Wang <xiyou.wangcong@gmail.com>
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: John Fastabend <john.fastabend@gmail.com>
Cc: Kevin Athey <kda@google.com>
Cc: Xiaotian Pei <xiaotian@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
120 lines
3.6 KiB
Plaintext
120 lines
3.6 KiB
Plaintext
Generic networking statistics for netlink users
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======================================================================
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Statistic counters are grouped into structs:
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Struct TLV type Description
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----------------------------------------------------------------------
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gnet_stats_basic TCA_STATS_BASIC Basic statistics
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gnet_stats_rate_est TCA_STATS_RATE_EST Rate estimator
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gnet_stats_queue TCA_STATS_QUEUE Queue statistics
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none TCA_STATS_APP Application specific
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Collecting:
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-----------
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Declare the statistic structs you need:
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struct mystruct {
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struct gnet_stats_basic bstats;
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struct gnet_stats_queue qstats;
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...
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};
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Update statistics, in dequeue() methods only, (while owning qdisc->running)
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mystruct->tstats.packet++;
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mystruct->qstats.backlog += skb->pkt_len;
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Export to userspace (Dump):
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---------------------------
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my_dumping_routine(struct sk_buff *skb, ...)
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{
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struct gnet_dump dump;
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if (gnet_stats_start_copy(skb, TCA_STATS2, &mystruct->lock, &dump,
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TCA_PAD) < 0)
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goto rtattr_failure;
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if (gnet_stats_copy_basic(&dump, &mystruct->bstats) < 0 ||
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gnet_stats_copy_queue(&dump, &mystruct->qstats) < 0 ||
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gnet_stats_copy_app(&dump, &xstats, sizeof(xstats)) < 0)
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goto rtattr_failure;
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if (gnet_stats_finish_copy(&dump) < 0)
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goto rtattr_failure;
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...
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}
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TCA_STATS/TCA_XSTATS backward compatibility:
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--------------------------------------------
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Prior users of struct tc_stats and xstats can maintain backward
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compatibility by calling the compat wrappers to keep providing the
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existing TLV types.
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my_dumping_routine(struct sk_buff *skb, ...)
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{
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if (gnet_stats_start_copy_compat(skb, TCA_STATS2, TCA_STATS,
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TCA_XSTATS, &mystruct->lock, &dump,
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TCA_PAD) < 0)
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goto rtattr_failure;
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...
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}
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A struct tc_stats will be filled out during gnet_stats_copy_* calls
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and appended to the skb. TCA_XSTATS is provided if gnet_stats_copy_app
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was called.
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Locking:
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--------
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Locks are taken before writing and released once all statistics have
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been written. Locks are always released in case of an error. You
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are responsible for making sure that the lock is initialized.
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Rate Estimator:
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--------------
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0) Prepare an estimator attribute. Most likely this would be in user
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space. The value of this TLV should contain a tc_estimator structure.
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As usual, such a TLV needs to be 32 bit aligned and therefore the
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length needs to be appropriately set, etc. The estimator interval
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and ewma log need to be converted to the appropriate values.
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tc_estimator.c::tc_setup_estimator() is advisable to be used as the
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conversion routine. It does a few clever things. It takes a time
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interval in microsecs, a time constant also in microsecs and a struct
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tc_estimator to be populated. The returned tc_estimator can be
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transported to the kernel. Transfer such a structure in a TLV of type
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TCA_RATE to your code in the kernel.
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In the kernel when setting up:
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1) make sure you have basic stats and rate stats setup first.
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2) make sure you have initialized stats lock that is used to setup such
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stats.
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3) Now initialize a new estimator:
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int ret = gen_new_estimator(my_basicstats,my_rate_est_stats,
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mystats_lock, attr_with_tcestimator_struct);
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if ret == 0
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success
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else
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failed
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From now on, every time you dump my_rate_est_stats it will contain
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up-to-date info.
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Once you are done, call gen_kill_estimator(my_basicstats,
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my_rate_est_stats) Make sure that my_basicstats and my_rate_est_stats
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are still valid (i.e still exist) at the time of making this call.
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Authors:
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--------
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Thomas Graf <tgraf@suug.ch>
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Jamal Hadi Salim <hadi@cyberus.ca>
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