[ltt-dev] PATCH [0/1]: Replace gettimeofday with clock_gettime

[Nils Carlson]

Comments below,

On May 25, 2010, at 4:31 PM, Pierre-Marc Fournier wrote:

> Thanks, comments below.
>
>
> On 05/24/2010 10:54 AM, Nils Carlson wrote:
>> This patch replaces gettimeofday with clock_gettime(CLOCK_MONOTONIC,)
>>
>> Signed-off-by: Nils Carlson<nils.carlson at ludd.ltu.se>
>>
>> diff --git a/include/ust/clock.h b/include/ust/clock.h
>> index d4b6a9d..bc26d26 100644
>> --- a/include/ust/clock.h
>> +++ b/include/ust/clock.h
>> @@ -18,6 +18,7 @@
>>  #ifndef UST_CLOCK_H
>>  #define UST_CLOCK_H
>>
>> +#include<time.h>
>>  #include<sys/time.h>
>>  #include<ust/kcompat/kcompat.h>
>>
>> @@ -25,7 +26,7 @@
>>
>>  /* There are two types of clocks that can be used.
>>     - TSC based clock
>> -   - gettimeofday() clock
>> +   - gettimeofday() clock - to guarantee monotonicity use  
>> clock_gettime
>>
>>     Microbenchmarks on Linux 2.6.30 on Core2 Duo 3GHz (functions are
>> inlined):
>>       Calls (100000000) to tsc(): 4004035641 cycles or 40 cycles/call
>> @@ -41,13 +42,13 @@
>>
>>  static __inline__ u64 trace_clock_read64(void)
>>  {
>> -       struct timeval tv;
>> +       struct timespec ts;
>>         u64 retval;
>>
>> -       gettimeofday(&tv, NULL);
>> -       retval = tv.tv_sec;
>> +       clock_gettime(CLOCK_MONOTONIC,&ts);
>> +       retval = ts.tv_sec;
>>         retval *= 1000000;
>> -       retval += tv.tv_usec;
>> +       retval += ts.tv_nsec / 1000;
>
> Any specific reason for truncating the nanoseconds here?

Only to provide the same fidelity as the previous code. I don't know  
enough
about how you use the timer, so I didn't take it upon myself to change  
the
resolution.

>
>>
>>         return retval;
>>  }
>> diff --git a/libust/Makefile.am b/libust/Makefile.am
>> index 2de5857..e357ad1 100644
>> --- a/libust/Makefile.am
>> +++ b/libust/Makefile.am
>> @@ -27,6 +27,7 @@ libust_la_LDFLAGS = -no-undefined -version-info  
>> 0:0:0
>>
>>  libust_la_LIBADD = \
>>         -lpthread \
>> +       -lrt \
>
> I guess this isn't supposed to be part of the patch?

It is. clock_gettime requires the realtime clock library.

>
>>         $(top_builddir)/snprintf/libustsnprintf.la \
>>         $(top_builddir)/libustcomm/libustcomm.la
>>
>>
>>
>>
>>
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