From owner-freebsd-hackers@freebsd.org  Sat Jul  9 10:47:17 2016
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From: Wojciech Puchar <wojtek@puchar.net>
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To: freebsd-hackers@freebsd.org
Subject: apache&EnableSendfile on = 100% CPU
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is it apache or possible kernel bug (FreeBSD 10)?

When i turn on EnableSendfile setting in apache config, the process 
handling http connection would use 100% CPU no matter if i transfer 1kB/s 
or 1GB/s.

turning it off fixes the problem.

where can i search for problem source?