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author | David Ahern <dsahern@gmail.com> | 2019-03-20 19:18:59 +0300 |
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committer | David S. Miller <davem@davemloft.net> | 2019-03-21 23:29:53 +0300 |
commit | 9ab948a91b2c2abc8e82845c0e61f4b1683e3a4f (patch) | |
tree | d096d05c00760a38c1d91b6f5be5bd91fc28a445 /include/net | |
parent | 12132768dc4a79be65af75ac6262117d0adf93f3 (diff) | |
download | linux-9ab948a91b2c2abc8e82845c0e61f4b1683e3a4f.tar.xz |
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 'include/net')
-rw-r--r-- | include/net/ip.h | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/include/net/ip.h b/include/net/ip.h index be3cad9c2e4c..aa09ae5f01a5 100644 --- a/include/net/ip.h +++ b/include/net/ip.h @@ -38,6 +38,10 @@ #define IPV4_MAX_PMTU 65535U /* RFC 2675, Section 5.1 */ #define IPV4_MIN_MTU 68 /* RFC 791 */ +extern unsigned int sysctl_fib_sync_mem; +extern unsigned int sysctl_fib_sync_mem_min; +extern unsigned int sysctl_fib_sync_mem_max; + struct sock; struct inet_skb_parm { |