I have this problem, especially when viewing webpages with video/flash in them. I ran the line from the previous comment, which indicates that it's caused by intel_drv.so. Attached the perf.data file.

Standard out:

# ========
# captured on: Thu May  2 15:39:02 2013
# hostname : .....
# os release : 3.8.0-19-generic
# perf version : 3.8.8
# arch : x86_64
# nrcpus online : 4
# nrcpus avail : 4
# cpudesc : Intel(R) Core(TM) i5-2450M CPU @ 2.50GHz
# cpuid : GenuineIntel,6,42,7
# total memory : 5997284 kB
# cmdline : /usr/bin/perf_3.8.0-19 record -f -g -a sleep 60 
# event : name = cycles, type = 0, config = 0x0, config1 = 0x0, config2 = 0x0, excl_usr = 0, excl_kern = 0, excl_host = 0, excl_guest = 1, precise_ip = 0, id = { 22, 23, 24, 25 }
# HEADER_CPU_TOPOLOGY info available, use -I to display
# HEADER_NUMA_TOPOLOGY info available, use -I to display
# pmu mappings: cpu = 4, software = 1, tracepoint = 2, uncore_cbox_0 = 6, uncore_cbox_1 = 7, breakpoint = 5
# ========
#
# Samples: 351K of event 'cycles'
# Event count (approx.): 217205974361
#
# Overhead          Command                    Shared Object                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                      Symbol
# ........  ...............  ...............................  ..........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................
#
    78.14%             Xorg  intel_drv.so                     [.] 0x000000000003781f                                                                                                                                                                                                                                                                                                                                                                                                                                           
                       |
                       --- 0x7f6a18cac81f