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From: "Jérémie Galarneau via lttng-dev" <lttng-dev@lists.lttng.org>
To: "lttng-dev@lists.lttng.org" <lttng-dev@lists.lttng.org>,
	Akhil Veeraghanta <akhil.veeraghanta@outlook.com>
Subject: Re: [lttng-dev] lttng-ust on arm64 getting bogged down by the getcpu syscall (taking more than 600ns per call)
Date: Wed, 12 Oct 2022 09:19:01 +0000	[thread overview]
Message-ID: <YT2PR01MB59842EC5E5A7DCED7D7C3C2FBC229@YT2PR01MB5984.CANPRD01.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <CO1PR03MB59371096D2E4AB93558EA072E5239@CO1PR03MB5937.namprd03.prod.outlook.com>


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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 when available.

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

Jérémie

--
Jérémie Galarneau
EfficiOS Inc.
https://www.efficios.com
________________________________
From: lttng-dev <lttng-dev-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 getcpu syscall (taking more than 600ns per call)

Hello!

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.
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

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

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      reply	other threads:[~2022-10-12  9:19 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-11 20:57 Akhil Veeraghanta via lttng-dev
2022-10-12  9:19 ` Jérémie Galarneau via lttng-dev [this message]

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