clock_gettime vdso issue

clock_gettime vdso issue

[zhenyu.ren]

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Hi,Team
   You may not feel how painful I am with a too old GLIBC which does NOT support vdso clock_gettime. Especially in ust case, trace_clock_read will call clock_gettime to record the time of every event. Does anyone know how to avoid system_call clock_gettime with this old GLIBC??Thanks in advancezhenyu.ren

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Re: clock_gettime vdso issue

[Jesper Derehag]

There has been discussions regarding adding capability to override the clock implementation.

If that support is arriving, you could always write your own (say a separate thread reading clock periodically and storing in a cache, then your own clock implementation could get that cached timestamp).
Obviously you would need to think very carefully about clock resolution and frequency for your clock thread, but it should from a performance point of view be big improvement..

Maybe Mathieu(?) could shed some light on the clock override?

/Jesper

________________________________
> Date: Thu, 26 Mar 2015 15:25:49 +0800 
> From: zhenyu.ren@aliyun.com 
> To: lttng-dev@lists.lttng.org 
> Subject: [lttng-dev] clock_gettime vdso issue 
> 
> 
> Hi,Team 
> 
> You may not feel how painful I am with a too old GLIBC which does 
> NOT support vdso clock_gettime. Especially in ust case, 
> trace_clock_read will call clock_gettime to record the time of every 
> event. 
> Does anyone know how to avoid system_call clock_gettime with this old GLIBC?? 
> 
> Thanks in advance 
> zhenyu.ren 
> 
> 
> _______________________________________________ lttng-dev mailing list 
> lttng-dev@lists.lttng.org 
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev 
 		 	   		  

Re: clock_gettime vdso issue

[Mathieu Desnoyers]

Yes, the clock override feature, as well as the getcpu override,
should be merged within lttng-ust and lttng-tools master branches
this week. Stay tuned!

Thanks,

Mathieu

----- Original Message -----
> There has been discussions regarding adding capability to override the clock
> implementation.
> 
> If that support is arriving, you could always write your own (say a separate
> thread reading clock periodically and storing in a cache, then your own
> clock implementation could get that cached timestamp).
> Obviously you would need to think very carefully about clock resolution and
> frequency for your clock thread, but it should from a performance point of
> view be big improvement..
> 
> Maybe Mathieu(?) could shed some light on the clock override?
> 
> /Jesper
> 
> ________________________________
> > Date: Thu, 26 Mar 2015 15:25:49 +0800
> > From: zhenyu.ren@aliyun.com
> > To: lttng-dev@lists.lttng.org
> > Subject: [lttng-dev] clock_gettime vdso issue
> > 
> > 
> > Hi,Team
> > 
> > You may not feel how painful I am with a too old GLIBC which does
> > NOT support vdso clock_gettime. Especially in ust case,
> > trace_clock_read will call clock_gettime to record the time of every
> > event.
> > Does anyone know how to avoid system_call clock_gettime with this old
> > GLIBC??
> > 
> > Thanks in advance
> > zhenyu.ren
> > 
> > 
> > _______________________________________________ lttng-dev mailing list
> > lttng-dev@lists.lttng.org
> > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
>  		 	   		  
> _______________________________________________
> lttng-dev mailing list
> lttng-dev@lists.lttng.org
> http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> 

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com