Mysql loads 4 cores 2800MHZ at 95%?

Question

MySQL

In general, a small online more than 100 people on average does not rise. About 4,000,000 requests per hour. Not so much.
But mysql loads all 4 cores into chips. The indexes are not broken. slow query 1 is empty. mysql log is empty.
in top, on average, the picture is as follows:

PID USER      PR     NI     VIRT     RES        SHR S        %CPU      %MEM      TIME+        COMMAND
2207 mysql     20   0      774m   217m   8168 S      320.6         5.3         137:26.32     mysqld

mytop showed 2 queries that it optimized now it's empty there. Where to look next?