<div class="__aliyun_email_body_block"><div  style="clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;">Hi, </span></div><div  style="clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;">   I know lttng-ust tracepoint process uses per cpu lockless ringbuffer algorithm for high performance so that it relies on getcpu() to return the cpu number on which the app is running.</span></div><div  style="clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;">   Unfortunately, I am working on arm that linux kernel does not support vdso getcpu() implemention and one getcpu() will take 200ns!!!</span></div><div  style="clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;">   My question is :</span></div><div  style="clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;">   1. do you have any advice for that?</span></div><div  style="clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;">   2. If I implement a cache-version for getcpu()(just like getcpu() implemention before kernel 2.6.23 ), what will happen during tracing process?  </span></div><div  style="clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;">      Since use of the cache could speed getcpu() calls, at the cost that there was a very small chance that the returned cpu number would be out of date, I am not sure whether the "wrong" cpu number will result in the tracing app crashing?</span></div><div  style="clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;"><br ></span></div><div  style="clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;">Thanks</span></div><div  style="clear:both;"><span  style="font-family:Tahoma,Arial,STHeiti,SimSun;font-size:14.0px;color:#000000;">zhenyu.ren</span></div></div>