Messages in this thread | | | Date | Tue, 18 Apr 2023 16:36:11 +0300 | Subject | Re: [PATCH RFC 0/5] perf: Add ioctl to emit sideband events | From | Adrian Hunter <> |
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On 18/04/23 09:18, Adrian Hunter wrote: > On 17/04/23 14:02, Peter Zijlstra wrote: >> On Fri, Apr 14, 2023 at 11:22:55AM +0300, Adrian Hunter wrote: >>> Hi >>> >>> Here is a stab at adding an ioctl for sideband events. >>> >>> This is to overcome races when reading the same information >>> from /proc. >> >> What races? Are you talking about reading old state in /proc the kernel >> delivering a sideband event for the new state, and then you writing the >> old state out? >> >> Surely that's something perf tool can fix without kernel changes? > > Yes, and it was a bit of a brain fart not to realise that. > > There may still be corner cases, where different kinds of events are > interdependent, perhaps NAMESPACES events vs MMAP events could > have ordering issues. > > Putting that aside, the ioctl may be quicker than reading from > /proc. I could get some numbers and see what people think. >
Here's a result with a quick hack to use the ioctl but without handling the buffer becoming full (hence the -m4M)
# ps -e | wc -l 1171 # perf.old stat -- perf.old record -o old.data --namespaces -a true [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 1.095 MB old.data (100 samples) ]
Performance counter stats for 'perf.old record -o old.data --namespaces -a true':
498.15 msec task-clock # 0.987 CPUs utilized 126 context-switches # 252.935 /sec 64 cpu-migrations # 128.475 /sec 4396 page-faults # 8.825 K/sec 1927096347 cycles # 3.868 GHz 4563059399 instructions # 2.37 insn per cycle 914232559 branches # 1.835 G/sec 6618052 branch-misses # 0.72% of all branches 9633787105 slots # 19.339 G/sec 4394300990 topdown-retiring # 38.8% Retiring 3693815286 topdown-bad-spec # 32.6% Bad Speculation 1692356927 topdown-fe-bound # 14.9% Frontend Bound 1544151518 topdown-be-bound # 13.6% Backend Bound
0.504636742 seconds time elapsed
0.158237000 seconds user 0.340625000 seconds sys
# perf.old stat -- perf.new record -o new.data -m4M --namespaces -a true [ perf record: Woken up 1 times to write data ] [ perf record: Captured and wrote 1.095 MB new.data (103 samples) ]
Performance counter stats for 'perf.new record -o new.data -m4M --namespaces -a true':
386.61 msec task-clock # 0.988 CPUs utilized 100 context-switches # 258.658 /sec 65 cpu-migrations # 168.128 /sec 4935 page-faults # 12.765 K/sec 1495905137 cycles # 3.869 GHz 3647660473 instructions # 2.44 insn per cycle 735822370 branches # 1.903 G/sec 5765668 branch-misses # 0.78% of all branches 7477722620 slots # 19.342 G/sec 3415835954 topdown-retiring # 39.5% Retiring 2748625759 topdown-bad-spec # 31.8% Bad Speculation 1221594670 topdown-fe-bound # 14.1% Frontend Bound 1256150733 topdown-be-bound # 14.5% Backend Bound
0.391472763 seconds time elapsed
0.141207000 seconds user 0.246277000 seconds sys
# ls -lh old.data -rw------- 1 root root 1.2M Apr 18 13:19 old.data # ls -lh new.data -rw------- 1 root root 1.2M Apr 18 13:19 new.data #
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