From: fwefew 4t4tg <7532yahoo@gmail.com>
To: users@dpdk.org
Subject: Re: Using rdtsc to timestamp RTT of packets
Date: Mon, 6 Mar 2023 12:33:06 -0500 [thread overview]
Message-ID: <CA+Tq66WFh+os7ib=Ysaw7VmsKP0_GP3b=gHZwBxDS2-fSE5EAA@mail.gmail.com> (raw)
In-Reply-To: <20230306085614.72951a6f@hermes.local>
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Using rdtsc to timestamp RTT of packets
Stephen/Gabor/Harry: Gents thanks for the guidance; this mailing list is
great. The message is rdtsc is just fine. Got it.
The command line (from Harry):
>lscpu | egrep "constant_tsc|nonstop_tsc"
is operationally ideal: specific, easy, and answers the issue of
invariance/constancy clearly.
On Mon, Mar 6, 2023 at 11:56 AM Stephen Hemminger <
stephen@networkplumber.org> wrote:
> On Sun, 5 Mar 2023 20:01:15 -0500
> fwefew 4t4tg <7532yahoo@gmail.com> wrote:
>
> > I think rdtsc does all this. But then I read [1]:
> >
> > - The TSC is not always invariant
> > - And of course context switches (if a thread is not pinned to a core)
> > will invalidate any time difference
> > - The TSC is not incremented when the processor enters a deep sleep. I
> > don't care about this because I'll turn off the power saving modes
> anyway
>
> Stack Overflow is only one step better than ChatGPT in giving
> partially correct answers.
>
> TSC is almost always works well on modern processors.
> The Linux kernel aligns all the TSC values for each core at boot up.
> It is invariant (derived from a single clock source) unless you have some
> poorly designed NUMA system. In the past, there were some CPU's that
> did bad things during suspend, but that is fixed in current generations.
>
> Bottom line: that advice is no longer true.
>
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prev parent reply other threads:[~2023-03-06 17:33 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-03-06 1:01 fwefew 4t4tg
2023-03-06 7:56 ` Gabor LENCSE
2023-03-06 9:46 ` Van Haaren, Harry
2023-03-06 16:56 ` Stephen Hemminger
2023-03-06 17:33 ` fwefew 4t4tg [this message]
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