Re: [Qemu-devel] [PATCH, RFC] Sparc: convert some debug printf statements to tracepoints

[Blue Swirl]

On Sun, Oct 10, 2010 at 6:01 PM, Artyom Tarasenko <address@hidden> wrote:
> On Sun, Oct 10, 2010 at 7:37 PM, Artyom Tarasenko <address@hidden> wrote:
>> On Sat, Oct 9, 2010 at 5:10 PM, Blue Swirl <address@hidden> wrote:
>>> Replace some debug printf statements with tracepoints.
>>>
>>> Signed-off-by: Blue Swirl <address@hidden>
>>> ---
>>> I think tracing way is more flexible than current conditional code. I
>>> remember wading through hundreds of megs of DPRINTF output looking for
>>> a clue about a specific event, so being able to control the trace
>>> dynamically is invaluable.
>>>
>>> Here's example simpletrace.py output:
>>> sparc64_translate 0.000 address=0x1fff0000040 paddr=0x1fff0000040
>>> vaddr=0x1fff0000000 mmu_idx=0x4 primary_context=0x0
>>> secondary_context=0x0
>>> sparc64_translate 24.017 address=0x1fff000bc50 paddr=0x1fff000bc50
>>> vaddr=0x1fff000a000 mmu_idx=0x4 primary_context=0x0
>>> secondary_context=0x0
>>> sparc64_translate 3.921 address=0x1fff000bc5c paddr=0x1fff000bc5c
>>> vaddr=0x1fff000a000 mmu_idx=0x2 primary_context=0x0
>>> secondary_context=0x0
>>> sparc64_translate 337.702 address=0x1fff000bf38 paddr=0x1fff000bf38
>>> vaddr=0x1fff000a000 mmu_idx=0x2 primary_context=0x0
>>> secondary_context=0x0
>>>
>>> There are problems #including "trace.h" from op_helper.c
>>> (qemu-common.h conflicts with dyngen-exec.h), otherwise this looks
>>> promising.
>>> ---
>>>  target-sparc/helper.c |   65 
>>> +++++++++++-------------------------------------
>>>  trace-events          |   10 +++++++
>>>  2 files changed, 25 insertions(+), 50 deletions(-)
>>>
>>> diff --git a/target-sparc/helper.c b/target-sparc/helper.c
>>> index aa1fd63..8078d92 100644
>>> --- a/target-sparc/helper.c
>>> +++ b/target-sparc/helper.c
>>> @@ -26,17 +26,11 @@
>>>  #include "cpu.h"
>>>  #include "exec-all.h"
>>>  #include "qemu-common.h"
>>> +#include "trace.h"
>>>
>>>  //#define DEBUG_MMU
>>>  //#define DEBUG_FEATURES
>>>
>>> -#ifdef DEBUG_MMU
>>
>> wouldn't it be better to keep the #ifdefs? Don't mmu functions have a
>> strong impact on the performance?
>
> After reading how the nop backed works, I take it back.

Even a full trace with all Sparc stuff enabled using simpletrace
backend seems to have very low overhead compared to printfs. I suppose
async I/O would lower the overhead even more.