diff options
author | David Ahern <dsahern@gmail.com> | 2019-03-20 09:18:59 -0700 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2019-03-21 13:29:53 -0700 |
commit | 9ab948a91b2c2abc8e82845c0e61f4b1683e3a4f (patch) | |
tree | d096d05c00760a38c1d91b6f5be5bd91fc28a445 /net | |
parent | 12132768dc4a79be65af75ac6262117d0adf93f3 (diff) |
ipv4: Allow amount of dirty memory from fib resizing to be controllable
fib_trie implementation calls synchronize_rcu when a certain amount of
pages are dirty from freed entries. The number of pages was determined
experimentally in 2009 (commit c3059477fce2d).
At the current setting, synchronize_rcu is called often -- 51 times in a
second in one test with an average of an 8 msec delay adding a fib entry.
The total impact is a lot of slow down modifying the fib. This is seen
in the output of 'time' - the difference between real time and sys+user.
For example, using 720,022 single path routes and 'ip -batch'[1]:
$ time ./ip -batch ipv4/routes-1-hops
real 0m14.214s
user 0m2.513s
sys 0m6.783s
So roughly 35% of the actual time to install the routes is from the ip
command getting scheduled out, most notably due to synchronize_rcu (this
is observed using 'perf sched timehist').
This patch makes the amount of dirty memory configurable between 64k where
the synchronize_rcu is called often (small, low end systems that are memory
sensitive) to 64M where synchronize_rcu is called rarely during a large
FIB change (for high end systems with lots of memory). The default is 512kB
which corresponds to the current setting of 128 pages with a 4kB page size.
As an example, at 16MB the worst interval shows 4 calls to synchronize_rcu
in a second blocking for up to 30 msec in a single instance, and a total
of almost 100 msec across the 4 calls in the second. The trade off is
allowing FIB entries to consume more memory in a given time window but
but with much better fib insertion rates (~30% increase in prefixes/sec).
With this patch and net.ipv4.fib_sync_mem set to 16MB, the same batch
file runs in:
$ time ./ip -batch ipv4/routes-1-hops
real 0m9.692s
user 0m2.491s
sys 0m6.769s
So the dead time is reduced to about 1/2 second or <5% of the real time.
[1] 'ip' modified to not request ACK messages which improves route
insertion times by about 20%
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net')
-rw-r--r-- | net/ipv4/fib_trie.c | 14 | ||||
-rw-r--r-- | net/ipv4/sysctl_net_ipv4.c | 9 |
2 files changed, 17 insertions, 6 deletions
diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c index a573e37e0615..1704f432de1f 100644 --- a/net/ipv4/fib_trie.c +++ b/net/ipv4/fib_trie.c @@ -183,14 +183,16 @@ struct trie { }; static struct key_vector *resize(struct trie *t, struct key_vector *tn); -static size_t tnode_free_size; +static unsigned int tnode_free_size; /* - * synchronize_rcu after call_rcu for that many pages; it should be especially - * useful before resizing the root node with PREEMPT_NONE configs; the value was - * obtained experimentally, aiming to avoid visible slowdown. + * synchronize_rcu after call_rcu for outstanding dirty memory; it should be + * especially useful before resizing the root node with PREEMPT_NONE configs; + * the value was obtained experimentally, aiming to avoid visible slowdown. */ -static const int sync_pages = 128; +unsigned int sysctl_fib_sync_mem = 512 * 1024; +unsigned int sysctl_fib_sync_mem_min = 64 * 1024; +unsigned int sysctl_fib_sync_mem_max = 64 * 1024 * 1024; static struct kmem_cache *fn_alias_kmem __ro_after_init; static struct kmem_cache *trie_leaf_kmem __ro_after_init; @@ -504,7 +506,7 @@ static void tnode_free(struct key_vector *tn) tn = container_of(head, struct tnode, rcu)->kv; } - if (tnode_free_size >= PAGE_SIZE * sync_pages) { + if (tnode_free_size >= sysctl_fib_sync_mem) { tnode_free_size = 0; synchronize_rcu(); } diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c index ba0fc4b18465..2316c08e9591 100644 --- a/net/ipv4/sysctl_net_ipv4.c +++ b/net/ipv4/sysctl_net_ipv4.c @@ -549,6 +549,15 @@ static struct ctl_table ipv4_table[] = { .mode = 0644, .proc_handler = proc_doulongvec_minmax, }, + { + .procname = "fib_sync_mem", + .data = &sysctl_fib_sync_mem, + .maxlen = sizeof(sysctl_fib_sync_mem), + .mode = 0644, + .proc_handler = proc_douintvec_minmax, + .extra1 = &sysctl_fib_sync_mem_min, + .extra2 = &sysctl_fib_sync_mem_max, + }, { } }; |