CPU increase in mod_cluster after updating to JBCS 2.4.37/mod_cluster 1.3.12

Issue

• We updated JBCS httpd to 2.4.37 and mod_cluster 1.3.12+. After this, we see a larger amount of CPU usage from httpd without application requests when many JBoss instances have joined the balancer. pstacks show the CPU usage in proxy_cluster_watchdog_func like below:

#0  0x00007f1bfe8dfc3d in poll () from /lib64/libc.so.6
#1  0x00007f1bff00afed in apr_wait_for_io_or_timeout () from /opt/httpd/lib/libapr-1.so.0
#2  0x00007f1bff001b50 in apr_socket_recv () from /opt/httpd/lib/libapr-1.so.0
#3  0x00007f1bff686a01 in socket_bucket_read () from /opt/httpd/lib/libaprutil-1.so.0
#4  0x000055c622ac8311 in ap_core_input_filter (f=0x7f1bcc018d50, b=0x7f1bcc018cd0, mode=<optimized out>, block=APR_BLOCK_READ, readbytes=5) at core_filters.c:235
#5  0x00007f1bf7c8e07e in logio_in_filter (f=<optimized out>, bb=0x7f1bcc018cd0, mode=<optimized out>, block=<optimized out>, readbytes=<optimized out>) at mod_logio.c:165
#6  0x00007f1bf23d02aa in bio_filter_in_read () from /opt/httpd/modules/mod_ssl.so
#7  0x00007f1bf1cfdced in bread_conv () from /opt/httpd/lib/libcrypto.so.1.1
#8  0x00007f1bf1cfcb1c in bio_read_intern () from /opt/httpd/lib/libcrypto.so.1.1
#9  0x00007f1bf1cfd113 in BIO_read () from /opt/httpd/lib/libcrypto.so.1.1
#10 0x00007f1bf21485f0 in ssl3_read_n () from /opt/httpd/lib/libssl.so.1.1
#11 0x00007f1bf214cb9e in ssl3_get_record () from /opt/httpd/lib/libssl.so.1.1
#12 0x00007f1bf214a363 in ssl3_read_bytes () from /opt/httpd/lib/libssl.so.1.1
#13 0x00007f1bf217d018 in tls_get_message_header () from /opt/httpd/lib/libssl.so.1.1
#14 0x00007f1bf2172825 in state_machine () from /opt/httpd/lib/libssl.so.1.1
#15 0x00007f1bf215e744 in SSL_do_handshake () from /opt/httpd/lib/libssl.so.1.1
#16 0x00007f1bf23d2b5b in ssl_io_filter_handshake () from /opt/httpd/modules/mod_ssl.so
#17 0x00007f1bf23d3826 in ssl_io_filter_output () from /opt/httpd/modules/mod_ssl.so
#18 0x00007f1bf23d094a in ssl_io_filter_coalesce () from /opt/httpd/modules/mod_ssl.so
#19 0x00007f1becd46361 in http_handle_cping_cpong () from /opt/httpd/modules/mod_proxy_cluster.so
#20 0x00007f1becd46cf0 in proxy_cluster_try_pingpong.isra.11 () from /opt/httpd/modules/mod_proxy_cluster.so
#21 0x00007f1becd47e74 in proxy_cluster_watchdog_func () from /opt/httpd/modules/mod_proxy_cluster.so
#22 0x00007f1bff00cba7 in dummy_worker () from /opt/httpd/lib/libapr-1.so.0
#23 0x00007f1bfedc5ea5 in start_thread () from /lib64/libpthread.so.0
#24 0x00007f1bfe8ea8dd in clone () from /lib64/libc.so.6