[lttng-dev] 答复： clock_gettime vdso issue

[Mathieu Desnoyers]

The feature is really just that: a way to let users override the clock 
source. Depending on the clock provided by the end user, it may or 
may not hurt resolution. 

The feature branches are here: 

https://github.com/compudj/lttng-ust-dev/tree/clock-getcpu-plugin 
https://github.com/compudj/lttng-tools-dev/tree/clock-plugin-ust 

Thanks, 

Mathieu 

----- Original Message -----

> 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 ?

> Thanks
> zhenyu.ren

> > ------------------------------------------------------------------
> 
> > 发件人：Mathieu Desnoyers <mathieu.desnoyers at efficios.com>
> 
> > 发送时间：2015年3月27日(星期五) 00:33
> 
> > 收件人：Jesper Derehag <jderehag at hotmail.com>
> 
> > 抄 送：zhenyu.ren <zhenyu.ren at aliyun.com>，lttng-dev
> > <lttng-dev at 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 at aliyun.com
> 
> > > > To: lttng-dev at 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 at lists.lttng.org
> 
> > > > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> 
> > >
> 
> > > _______________________________________________
> 
> > > lttng-dev mailing list
> 
> > > lttng-dev at lists.lttng.org
> 
> > > http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev
> 
> > >
> 

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