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boundary="===============3001479882005981377==" Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" --===============3001479882005981377== Content-Language: en-CA Content-Type: multipart/alternative; boundary="_000_YT2PR01MB59842EC5E5A7DCED7D7C3C2FBC229YT2PR01MB5984CANP_" --_000_YT2PR01MB59842EC5E5A7DCED7D7C3C2FBC229YT2PR01MB5984CANP_ Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Hi, I think the first problem you will run into is that rseq is only available = on kernels 4.18+. As far as I know, starting with glibc 2.35, getcpu() defers to using rseq w= hen available. Is there a way you can upgrade these two components and see if the overhead= is reduced? J=E9r=E9mie -- J=E9r=E9mie Galarneau EfficiOS Inc. https://www.efficios.com ________________________________ From: lttng-dev on behalf of Akhil Veer= aghanta via lttng-dev Sent: October 11, 2022 16:57 To: lttng-dev@lists.lttng.org Subject: [lttng-dev] lttng-ust on arm64 getting bogged down by the getcpu s= yscall (taking more than 600ns per call) Hello! I've run into an issue with getcpu not having a vsdo implementation and tak= ing anywhere from 600ns to 80us (avg 1 us) when using lttng-ust tracepoints= . I am on lttng v2.13 and kernel version 4.9.253-l4t, running on a jetson (ar= m64). I was digging around and found that rseq might be the recommended nex= t step I am wondering: 1. Are there examples of using rseq system call to replace getcpu 2. Are there any existing patches that I can apply to get better getcpu = performance Thanks in advance, Akhil --_000_YT2PR01MB59842EC5E5A7DCED7D7C3C2FBC229YT2PR01MB5984CANP_ Content-Type: text/html; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Hi,

I think the first problem you will run into is that rseq is only available = on kernels 4.18+.

As far as I know, starting with glibc 2.35, getcpu() defers to using rseq w= hen available.

Is there a way you can upgrade these two components and see if the overhead= is reduced?

J=E9r=E9mie

--
J=E9r=E9mie Galarneau
EfficiOS Inc.
https://www.efficios.com
From: lttng-dev <lttng-d= ev-bounces@lists.lttng.org> on behalf of Akhil Veeraghanta via lttng-dev= <lttng-dev@lists.lttng.org>
Sent: October 11, 2022 16:57
To: lttng-dev@lists.lttng.org <lttng-dev@lists.lttng.org>
Subject: [lttng-dev] lttng-ust on arm64 getting bogged down by the g= etcpu syscall (taking more than 600ns per call)
 
Hello!

I've run into an issue with getcpu not having a vsdo implementation and tak= ing anywhere from 600ns to 80us (avg 1 us) when using lttng-ust tracepoints= . 
I am on lttng v2.13 and kernel version 4.9.253-l4t, running on a jetso= n (arm64). I was digging around and found that rseq might be the recommende= d next step

I am wondering:
  1. Are there examples of using rseq system call to replace= getcpu
  2. Are there any existing patches that I can apply to get better getc= pu performance
Thanks in advance,
Akhil
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