Re: [patch] Performance Counters for Linux, v2
From: Arjan van de Ven
Date: Sun Dec 07 2008 - 20:48:27 EST
On Mon, 8 Dec 2008 02:22:12 +0100
Ingo Molnar <mingo@xxxxxxx> wrote:
>
> [ Performance counters are special hardware registers available on
> most modern CPUs. These register count the number of certain types of
> hw events: such as instructions executed, cachemisses suffered, or
> branches mis-predicted, without slowing down the kernel or
> applications. These registers can also trigger interrupts when a
> threshold number of events have passed - and can thus be used to
> profile the code that runs on that CPU. ]
>
> This is version 2 of our Performance Counters subsystem
> implementation.
>
> The biggest user-visible change in this release is a new user-space
> text-mode profiling utility that is based on this code: KernelTop.
>
> KernelTop can be downloaded from:
>
> http://redhat.com/~mingo/perfcounters/kerneltop.c
>
> It's a standalone .c file that needs no extra libraries - it only
> needs a CONFIG_PERF_COUNTERS=y kernel to run on.
>
> This utility is intended for kernel developers - it's basically a
> dynamic kernel profiler that gets hardware counter events dispatched
> to it continuously, which it feeds into a histogram and outputs it
> periodically.
>
I played with this a little, and while it works neat, I wanted a
feature added where it shows a detailed profile for the top function.
I've hacked this in quickly (the usability isn't all that great yet)
and put the source code up at
http://www.tglx.de/~arjan/kerneltop-0.02.tar.gz
with this it looks like this:
$ sudo ./kerneltop --vmlinux=/home/arjan/linux-2.6.git/vmlinux
------------------------------------------------------------------------------
KernelTop: 274 irqs/sec [NMI, 1000000 cycles], (all, 2 CPUs)
------------------------------------------------------------------------------
events RIP kernel function
______ ________________ _______________
230 - 00000000c04189e9 : read_hpet
82 - 00000000c0409439 : mwait_idle_with_hints
77 - 00000000c051a7b7 : acpi_os_read_port
52 - 00000000c053cb3a : acpi_idle_enter_bm
38 - 00000000c0418d93 : hpet_next_event
19 - 00000000c051a802 : acpi_os_write_port
14 - 00000000c04f8704 : __copy_to_user_ll
13 - 00000000c0460c20 : get_page_from_freelist
7 - 00000000c041c96c : kunmap_atomic
5 - 00000000c06a30d2 : _spin_lock [joydev]
4 - 00000000c04f79b7 : vsnprintf [snd_seq]
4 - 00000000c06a3048 : _spin_lock_irqsave [pcspkr]
3 - 00000000c0403b3c : irq_entries_start
3 - 00000000c0423fee : run_rebalance_domains
3 - 00000000c0425e2c : scheduler_tick
3 - 00000000c0430938 : get_next_timer_interrupt
3 - 00000000c043cdfa : __update_sched_clock
3 - 00000000c0448b14 : update_iter
2 - 00000000c04304bd : run_timer_softirq
Showing details for read_hpet
0 c04189e9 <read_hpet>:
2 c04189e9: a1 b0 e0 89 c0 mov 0xc089e0b0,%eax
0
0 /*
0 * Clock source related code
0 */
0 static cycle_t read_hpet(void)
0 {
1 c04189ee: 55 push %ebp
0 c04189ef: 89 e5 mov %esp,%ebp
1 c04189f1: 05 f0 00 00 00 add $0xf0,%eax
0 c04189f6: 8b 00 mov (%eax),%eax
0 return (cycle_t)hpet_readl(HPET_COUNTER);
0 }
300 c04189f8: 31 d2 xor %edx,%edx
0 c04189fa: 5d pop %ebp
0 c04189fb: c3 ret
0
As is usual with profile outputs, the cost for the function always gets added to the instruction after
the really guilty one. I'd move the count one back, but this is hard if the previous instruction was a
(conditional) jump...
--
Arjan van de Ven Intel Open Source Technology Centre
For development, discussion and tips for power savings,
visit http://www.lesswatts.org
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