答复： clock_gettime vdso issue

["zhenyu.ren" <zhenyu.ren@aliyun.com>]

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Hello  Are there any documents about what the clock override feature is? It seems that the feature will hurt time resolution,doesn't it?In fact,I will try to get the symbol addr of  __vdso_clock_gettime just like the same way glibc does with __vdso_gettimeofday.Is there any other cheaper way to call    __vdso_clock_gettime  ?
Thankszhenyu.ren
------------------------------------------------------------------发件人：Mathieu Desnoyers <mathieu.desnoyers@efficios.com>发送时间：2015年3月27日(星期五) 00:33收件人：Jesper Derehag <jderehag@hotmail.com>抄　送：zhenyu.ren <zhenyu.ren@aliyun.com>，lttng-dev <lttng-dev@lists.lttng.org>主　题：Re: [lttng-dev] clock_gettime vdso issue
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
> > 
> > 
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-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com

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