From: "Geva, Erez" <erez.geva.ext@siemens.com>
To: Vinicius Costa Gomes <vinicius.gomes@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
Cong Wang <xiyou.wangcong@gmail.com>,
"David S . Miller" <davem@davemloft.net>,
Jakub Kicinski <kuba@kernel.org>,
Jamal Hadi Salim <jhs@mojatatu.com>,
Jiri Pirko <jiri@resnulli.us>, Andrei Vagin <avagin@gmail.com>,
Dmitry Safonov <0x7f454c46@gmail.com>,
"Eric W . Biederman" <ebiederm@xmission.com>,
Ingo Molnar <mingo@kernel.org>,
John Stultz <john.stultz@linaro.org>,
Michal Kubecek <mkubecek@suse.cz>,
Oleg Nesterov <oleg@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Richard Cochran <richardcochran@gmail.com>,
Stephen Boyd <sboyd@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Vladis Dronov <vdronov@redhat.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Frederic Weisbecker <frederic@kernel.org>,
Eric Dumazet <edumazet@google.com>
Cc: Jesus Sanchez-Palencia <jesus.sanchez-palencia@intel.com>,
Vedang Patel <vedang.patel@intel.com>,
"Sudler, Simon" <simon.sudler@siemens.com>,
"Meisinger, Andreas" <andreas.meisinger@siemens.com>,
"Bucher, Andreas" <andreas.bucher@siemens.com>,
"henning.schild@siemens.com" <henning.schild@siemens.com>,
"jan.kiszka@siemens.com" <jan.kiszka@siemens.com>,
"Zirkler, Andreas" <andreas.zirkler@siemens.com>,
"Sakic, Ermin" <ermin.sakic@siemens.com>,
"anninh.nguyen@siemens.com" <anninh.nguyen@siemens.com>,
"Saenger, Michael" <michael.saenger@siemens.com>,
"Maehringer, Bernd" <bernd.maehringer@siemens.com>,
"gisela.greinert@siemens.com" <gisela.greinert@siemens.com>,
Erez Geva <ErezGeva2@gmail.com>
Subject: Re: [PATCH 0/7] TC-ETF support PTP clocks series
Date: Fri, 2 Oct 2020 19:56:50 +0000 [thread overview]
Message-ID: <VI1PR10MB2446AE70D793A5DD8490A5B9AB310@VI1PR10MB2446.EURPRD10.PROD.OUTLOOK.COM> (raw)
In-Reply-To: <87eemg5u5i.fsf@intel.com>
On 02/10/2020 21:01, Vinicius Costa Gomes wrote:
> Hi Erez,
>
> Erez Geva <erez.geva.ext@siemens.com> writes:
>
>> Add support for using PTP clock with
>> Traffic control Earliest TxTime First (ETF) Qdisc.
>>
>> Why do we need ETF to use PTP clock?
>> Current ETF requires to synchronization the system clock
>> to the PTP Hardware clock (PHC) we want to send through.
>> But there are cases that we can not synchronize the system clock with
>> the desire NIC PHC.
>> 1. We use several NICs with several PTP domains that our device
>> is not allowed to be PTP master.
>> And we are not allowed to synchronize these PTP domains.
>> 2. We are using another clock source which we need for our system.
>> Yet our device is not allowed to be PTP master.
>> Regardless of the exact topology, as the Linux tradition is to allow
>> the user the freedom to choose, we propose a patch that will allow
>> the user to configure the TC-ETF with a PTP clock as well as
>> using the system clock.
>> * NOTE: we do encourage the users to synchronize the system clock with
>> a PTP clock.
>> As the ETF watchdog uses the system clock.
>> Synchronizing the system clock with a PTP clock will probably
>> reduce the frequency different of the PHC and the system clock.
>> As sequence, the user might be able to reduce the ETF delta time
>> and the packets latency cross the network.
>>
>> Follow the decision to derive a dynamic clock ID from the file description
>> of an opened PTP clock device file.
>> We propose a simple way to use the dynamic clock ID with the ETF Qdisc.
>> We will submit a patch to the "tc" tool from the iproute2 project
>> once this patch is accepted.
>>
>
> In addition to what Thomas said, I would like to add some thoughts
> (mostly re-wording some of Thomas' comments :-)).
>
> I think that there's an underlying problem/limitation that is the cause
> of the issue (or at least a step in the right direction) you are trying
> to solve: the issue is that PTP clocks can't be used as hrtimers.
>
> I didn't spend a lot of time thinking about how to solve this (the only
> thing that comes to mind is having a timecounter, or similar, "software
> view" over the PHC clock).
>
> Anyway, my feeling is that until this is solved, we would only be
> working around the problem, and creating even more hard to handle corner
> cases.
>
>
> Cheers,
>
You are right.
Thanks for the insight.
Erez
next prev parent reply other threads:[~2020-10-02 19:56 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-01 20:51 [PATCH 0/7] TC-ETF support PTP clocks series Erez Geva
2020-10-01 20:51 ` [PATCH 1/7] POSIX clock ID check function Erez Geva
2020-10-01 21:56 ` Thomas Gleixner
2020-10-01 20:51 ` [PATCH 2/7] Function to retrieve main clock state Erez Geva
2020-10-01 22:05 ` Thomas Gleixner
2020-10-02 0:19 ` Thomas Gleixner
2020-10-01 20:51 ` [PATCH 3/7] Functions to fetch POSIX dynamic clock object Erez Geva
2020-10-01 23:35 ` Thomas Gleixner
2020-10-01 20:51 ` [PATCH 4/7] Fix qdisc_watchdog_schedule_range_ns range check Erez Geva
2020-10-01 22:44 ` Thomas Gleixner
2020-10-01 20:51 ` [PATCH 5/7] Traffic control using high-resolution timer issue Erez Geva
2020-10-01 23:07 ` Thomas Gleixner
2020-10-01 20:51 ` [PATCH 6/7] TC-ETF code improvements Erez Geva
2020-10-01 20:51 ` [PATCH 7/7] TC-ETF support PTP clocks Erez Geva
2020-10-02 0:33 ` Thomas Gleixner
2020-10-02 11:05 ` Geva, Erez
2020-10-02 19:01 ` [PATCH 0/7] TC-ETF support PTP clocks series Vinicius Costa Gomes
2020-10-02 19:56 ` Geva, Erez [this message]
2020-10-03 0:10 ` Thomas Gleixner
2020-10-09 11:17 ` AW: " Meisinger, Andreas
2020-10-09 15:39 ` Thomas Gleixner
2020-10-14 9:12 Meisinger, Andreas
2020-10-15 23:16 ` Thomas Gleixner
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=VI1PR10MB2446AE70D793A5DD8490A5B9AB310@VI1PR10MB2446.EURPRD10.PROD.OUTLOOK.COM \
--to=erez.geva.ext@siemens.com \
--cc=0x7f454c46@gmail.com \
--cc=ErezGeva2@gmail.com \
--cc=andreas.bucher@siemens.com \
--cc=andreas.meisinger@siemens.com \
--cc=andreas.zirkler@siemens.com \
--cc=anninh.nguyen@siemens.com \
--cc=avagin@gmail.com \
--cc=bernd.maehringer@siemens.com \
--cc=bigeasy@linutronix.de \
--cc=davem@davemloft.net \
--cc=ebiederm@xmission.com \
--cc=edumazet@google.com \
--cc=ermin.sakic@siemens.com \
--cc=frederic@kernel.org \
--cc=gisela.greinert@siemens.com \
--cc=henning.schild@siemens.com \
--cc=jan.kiszka@siemens.com \
--cc=jesus.sanchez-palencia@intel.com \
--cc=jhs@mojatatu.com \
--cc=jiri@resnulli.us \
--cc=john.stultz@linaro.org \
--cc=kuba@kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=michael.saenger@siemens.com \
--cc=mingo@kernel.org \
--cc=mkubecek@suse.cz \
--cc=netdev@vger.kernel.org \
--cc=oleg@redhat.com \
--cc=peterz@infradead.org \
--cc=richardcochran@gmail.com \
--cc=sboyd@kernel.org \
--cc=simon.sudler@siemens.com \
--cc=tglx@linutronix.de \
--cc=vdronov@redhat.com \
--cc=vedang.patel@intel.com \
--cc=vinicius.gomes@intel.com \
--cc=xiyou.wangcong@gmail.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).