oprofile and ARM A9 hardware counter

[Ming Lei]

Hi,

On Mon, Jan 30, 2012 at 1:36 AM, stephane eranian
<eranian at googlemail.com> wrote:
> Hi,
>
> Ok, so I did a few more tests and there is a serious issue when sampling
> in frequency mode (the default). I noticed wrong number of samples, so
> I investigated this some more and instrumented the perf_event kernel code.
> I found some erratic timer ticks causing broken period adjustments.
>
> In fact, the problem is visible using top.
> I am running a noploop program on CPU0 and nothing else besides top.
> The noploop program  does: for(;;);. That is 100% user. On a 2-way

Sometimes it is not 100% user, for example irq/exception handling...

> system otherwise idle, I expect top to return 50% user 50% idle.
>
> Top with the commit:
>
> top - 16:19:21 up 5 min,  1 user,  load average: 0.23, 0.15, 0.07
> Tasks:  70 total,   2 running,  68 sleeping,   0 stopped,   0 zombie
> Cpu(s): 31.1%us,  2.0%sy,  0.0%ni, 66.2%id,  0.0%wa,  0.0%hi,  0.7%si,  0.0%st
>            ^^^^^^^^ That's WRONG

Did you reproduce the issue each time or just occasionally?

Looks no such issue on my board with 3.3-rc1 plus the 5 extra pmu/emu patches.

top - 00:59:15 up 7 min,  1 user,  load average: 1.00, 0.73, 0.35
Tasks:  56 total,   2 running,  54 sleeping,   0 stopped,   0 zombie
Cpu(s): 42.6%us,  0.2%sy,  0.0%ni, 56.8%id,  0.0%wa,  0.0%hi,  0.4%si,  0.0%st
Mem:   1013560k total,    50960k used,   962600k free,     6272k buffers
Swap:        0k total,        0k used,        0k free,    29036k cached

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
 1355 root      20   0  1460  260  216 R   99  0.0   5:07.38 busy
  532 root      20   0     0    0    0 S    0  0.0   0:00.23 kworker/1:1
 1356 root      20   0  2552 1120  916 R    0  0.1   0:01.93 top

>
> Mem:    940292k total,    74984k used,   865308k free,     8020k buffers
> Swap:   524240k total,        0k used,   524240k free,    37420k cached
>
>  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>  3770 eranian   20   0 644 160 128 R   99  0.0   0:14.21 noploop
>  3771 eranian   20   0  2184 1052  804 R    2  0.1   0:00.32 top
>    1 root      20   0  2564 1528  952 S    0  0.2   0:01.26 init
>
>
> I removed that one liner patch from Ming. The one fiddling with the
> clockdomains:
>
> --- a/arch/arm/mach-omap2/clockdomains44xx_data.c
> +++ b/arch/arm/mach-omap2/clockdomains44xx_data.c
> @@ -390,7 +390,7 @@ static struct clockdomain emu_sys_44xx_clkdm = {
>        .prcm_partition   = OMAP4430_PRM_PARTITION,
>        .cm_inst          = OMAP4430_PRM_EMU_CM_INST,
>        .clkdm_offs       = OMAP4430_PRM_EMU_CM_EMU_CDOFFS,
> -       .flags            = CLKDM_CAN_HWSUP,
> +       .flags            = CLKDM_CAN_SWSUP,

The patch should not affect timer tick logic, and what the patch does is
just to revert the commit [1]  wrt. emu clock domain.

>
> When I rerun, the test, it now work:
>
> top - 16:02:51 up 15 min,  1 user,  load average: 1.02, 0.46, 0.21
> Tasks:  70 total,   2 running,  68 sleeping,   0 stopped,   0 zombie
> Cpu(s): 47.2%us,  1.0%sy,  0.0%ni, 50.8%id,  0.0%wa,  0.0%hi,  1.0%si,  0.0%st
>           ^^^^^^^^ close enough (in it stabilize somehow around 49%
> which is good)
>
> Mem:    940292k total,    75288k used,   865004k free,     8004k buffers
> Swap:   524240k total,        0k used,   524240k free,    37408k cached
>
>  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
>  3771 eranian   20   0 644 160 128 R  100  0.0   0:34.44 noploop
>
> Although the patch fixes PMU interrupts, it breaks the timer tick logic somehow.
> The perf problem is related to timer tick.
>
> I am hoping that the tradeoff is not:
>     PMU interrupts but broken timer ticks
> vs.
>    No PMU interrupts but working timer ticks



[1], 3c50729b3fa1cd8ca1f347e6caf1081204cf1a7c
ARM: OMAP4: PM: Initialise all the clockdomains to supported states

thanks
--
Ming Lei