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Mon, 3 Jul 2023 03:20:15 -0400 (EDT) From: Thomas Monjalon <thomas@monjalon.net> To: Dongdong Liu <liudongdong3@huawei.com>, fengchengwen <fengchengwen@huawei.com> Cc: Bruce Richardson <bruce.richardson@intel.com>, dev@dpdk.org, Ferruh Yigit <ferruh.yigit@amd.com>, andrew.rybchenko@oktetlabs.ru, ciara.power@intel.com, kevin.laatz@intel.com, david.marchand@redhat.com Subject: Re: [PATCH v5 2/2] ethdev: support xstats reset telemetry command Date: Mon, 03 Jul 2023 09:20:13 +0200 Message-ID: <18761354.fAMKPKieAE@thomas> In-Reply-To: <c6ed23e5-d96a-5862-7e9c-1714437d6311@huawei.com> References: <20221219090723.29356-1-fengchengwen@huawei.com> <12802674.ZYm5mLc6kN@thomas> <c6ed23e5-d96a-5862-7e9c-1714437d6311@huawei.com> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions <dev.dpdk.org> List-Unsubscribe: <https://mails.dpdk.org/options/dev>, <mailto:dev-request@dpdk.org?subject=unsubscribe> List-Archive: <http://mails.dpdk.org/archives/dev/> List-Post: <mailto:dev@dpdk.org> List-Help: <mailto:dev-request@dpdk.org?subject=help> List-Subscribe: <https://mails.dpdk.org/listinfo/dev>, <mailto:dev-request@dpdk.org?subject=subscribe> Errors-To: dev-bounces@dpdk.org 03/07/2023 05:58, fengchengwen: > > On 2023/2/20 21:05, Thomas Monjalon wrote: > > 17/02/2023 10:44, fengchengwen: > >> On 2023/2/16 20:54, Bruce Richardson wrote: > >>> On Thu, Feb 16, 2023 at 08:42:34PM +0800, fengchengwen wrote: > >>>> On 2023/2/16 20:06, Ferruh Yigit wrote: > >>>>> On 2/16/2023 11:53 AM, fengchengwen wrote: > >>>>>> On 2023/2/15 11:19, Dongdong Liu wrote: > >>>>>>> Hi Chengwen > >>>>>>> > >>>>>>> On 2023/2/9 10:32, Chengwen Feng wrote: > >>>>>>>> The xstats reset is useful for debugging, so add it to the ethdev > >>>>>>>> telemetry command lists. > >>>>>>>> > >>>>>>>> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com> > >>>>>>> This patch looks good, so > >>>>>>> Reviewed-by: Dongdong Liu <liudongdong3@huawei.com> > >>>>>>> > >>>>>>> A minior question > >>>>>>> Do we need to support stats reset ? > >>>>>> > >>>>>> Stats is contained by xstats, and future direction I think is xstats. > >>>>>> So I think we don't need support stats reset. > >>>>>> > >>>>> > >>>>> I have similar question with Dongdong, readonly values are safe for > >>>>> telemetry, but modifying data can be more tricky since we don't have > >>>>> locking in ethdev APIs, this can cause concurrency issues. > >>>> > >>>> Yes, it indeed has concurrency issues. > >>>> > >>>>> > >>>>> Overall do we want telemetry go that way and become something that > >>>>> alters ethdev data/config? > >>>> > >>>> There are at least two part of data: config and status. > >>>> For stats (which belong status data) could help for debugging, I think it's acceptable. > >>>> > >>>> As for concurrency issues. People should know what to do and when to do, just like > >>>> the don't invoke config API (e.g. dev_configure/dev_start/...) concurrency. > >>>> > >>> While this is probably ok for now, I think in next release we should look > >>> to add some sort of support for locking for destructive ops in a future > >>> release. For example, we could: > >>> > >>> 1. Add support for marking a callback as "destructive" and only allow it to > >>> be called if only one connection is present or > >>> > >>> 2. Make it possible for callbacks to query the number of connections so > >>> that the callback itself is non-destructive in more than one connection is > >>> open. > >>> > >>> [Both of these will require locking support so that new connections aren't > >>> openned when the callback is in-flight!] > >> > >> Except telemetry, the application may have other console could execute DPDK API. > >> So I think trying to keep it simple, it's up to the user to invoke. > > > > No, the user should not be responsible for concurrency issues. > > We can ask the app developper to take care, > > but not to the user who has no control on what happens in the app. > > > > On a more general note, I feel the expansion of telemetry is not controlled enough. > > I would like to stop on adding more telemetry until we have a clear guideline > > about what is telemetry for and how to use it. > > Hi Thomas, > > Should this be discussed on TB? What would be your question exactly?