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SubjectLLC cache miss increases with the increases of hugepages
Date
Hi,

I did a network forward test with ovs-dpdk, and found that LLC cache miss
increases with the increases of hugepages. ovs-dpdk only use 4 hugepages,
hugepage size is 1G.Why LLC cache miss increases ? I just echo more hugepages
but haven't been used yet.

some informations:

CPU: Intel(R) Xeon(R) CPU E5-2620 v3@ 2.40GHz
L1d cache: 32K
L1i cache: 32K
L2 cache: 256K
L3 cache: 15360K

echo 10 > /proc/sys/vm/nr_hugepages
ovs-dpdk's LLC-load-misses:3.88%
ovs-dpdk's iTLB-load-misses: 4.37%


echo 100 > /proc/sys/vm/nr_hugepages
reboot VM restart test.
ovs-dpdk's LLC-load-misses:31.55%
ovs-dpdk's iTLB-load-misses: 36.36%

I use perf to watch LLC-loads when not run test:

Samples: 1M of event 'LLC-loads', Event count (approx.): 57240206
Overhead Shared Object Symbol
9.19% [kernel] [k] copy_page_rep
5.03% [kernel] [k] ktime_get
4.06% [unknown] [.] 0x000000000043e39d
2.65% bash [.] 0x000000000003e39d
2.13% [kernel] [k] rcu_check_callbacks

The function copy_page_rep seems like would prefetch all hugepages?

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