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Hi,</div>
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I think the first problem you will run into is that rseq is only available on kernels 4.18+.</div>
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As far as I know, starting with glibc 2.35, getcpu() defers to using rseq when available.</div>
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Is there a way you can upgrade these two components and see if the overhead is reduced?</div>
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Jérémie</div>
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Jérémie Galarneau</div>
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<div>EfficiOS Inc.</div>
<a href="https://www.efficios.com">https://www.efficios.com</a><br>
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<div id="divRplyFwdMsg" dir="ltr"><font face="Calibri, sans-serif" style="font-size:11pt" color="#000000"><b>From:</b> lttng-dev <lttng-dev-bounces@lists.lttng.org> on behalf of Akhil Veeraghanta via lttng-dev <lttng-dev@lists.lttng.org><br>
<b>Sent:</b> October 11, 2022 16:57<br>
<b>To:</b> lttng-dev@lists.lttng.org <lttng-dev@lists.lttng.org><br>
<b>Subject:</b> [lttng-dev] lttng-ust on arm64 getting bogged down by the getcpu syscall (taking more than 600ns per call)</font>
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Hello!<br>
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I've run into an issue with getcpu not having a vsdo implementation and taking anywhere from 600ns to 80us (avg 1 us) when using lttng-ust tracepoints. </div>
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I am on lttng v2.13 and kernel version 4.9.253-l4t, running on a jetson (arm64). I was digging around and found that rseq might be the recommended next step<br>
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I am wondering:</div>
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<li><span style="color:rgb(0,0,0); font-family:Calibri,Helvetica,sans-serif; font-size:12pt">Are there examples of using rseq system call to replace getcpu</span><br>
</li><li>Are there any existing patches that I can apply to get better getcpu performance</li></ol>
<div>Thanks in advance,</div>
<div>Akhil</div>
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