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Tue, 22 Sep 2020 13:34:06 +0000 (UTC) Received: from [10.10.115.78] (ovpn-115-78.rdu2.redhat.com [10.10.115.78]) by smtp.corp.redhat.com (Postfix) with ESMTPS id ABACC614F5; Tue, 22 Sep 2020 13:34:03 +0000 (UTC) Subject: Re: [RFC][Patch v1 2/3] i40e: limit msix vectors based on housekeeping CPUs To: Frederic Weisbecker , bhelgaas@google.com Cc: Jesse Brandeburg , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-pci@vger.kernel.org, mtosatti@redhat.com, sassmann@redhat.com, jeffrey.t.kirsher@intel.com, jacob.e.keller@intel.com, jlelli@redhat.com, hch@infradead.org, mike.marciniszyn@intel.com, dennis.dalessandro@intel.com, thomas.lendacky@amd.com, jerinj@marvell.com, mathias.nyman@intel.com, jiri@nvidia.com References: <20200909150818.313699-1-nitesh@redhat.com> <20200909150818.313699-3-nitesh@redhat.com> <20200917112359.00006e10@intel.com> <20200921225834.GA30521@lenoir> <65513ee8-4678-1f96-1850-0e13dbf1810c@redhat.com> <20200922095440.GA5217@lenoir> From: Nitesh Narayan Lal Autocrypt: addr=nitesh@redhat.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200922095440.GA5217@lenoir> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=nitesh@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="PDZV0yVtrsnz8iCpGtGumojvMZCcYC0xg" Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --PDZV0yVtrsnz8iCpGtGumojvMZCcYC0xg Content-Type: multipart/mixed; boundary="x5qKUNoegkyIUmDvOHigPup1eCGwUT80c" --x5qKUNoegkyIUmDvOHigPup1eCGwUT80c Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US On 9/22/20 5:54 AM, Frederic Weisbecker wrote: > On Mon, Sep 21, 2020 at 11:08:20PM -0400, Nitesh Narayan Lal wrote: >> On 9/21/20 6:58 PM, Frederic Weisbecker wrote: >>> On Thu, Sep 17, 2020 at 11:23:59AM -0700, Jesse Brandeburg wrote: >>>> Nitesh Narayan Lal wrote: >>>> >>>>> In a realtime environment, it is essential to isolate unwanted IRQs f= rom >>>>> isolated CPUs to prevent latency overheads. Creating MSIX vectors onl= y >>>>> based on the online CPUs could lead to a potential issue on an RT set= up >>>>> that has several isolated CPUs but a very few housekeeping CPUs. This= is >>>>> because in these kinds of setups an attempt to move the IRQs to the >>>>> limited housekeeping CPUs from isolated CPUs might fail due to the pe= r >>>>> CPU vector limit. This could eventually result in latency spikes beca= use >>>>> of the IRQ threads that we fail to move from isolated CPUs. >>>>> >>>>> This patch prevents i40e to add vectors only based on available >>>>> housekeeping CPUs by using num_housekeeping_cpus(). >>>>> >>>>> Signed-off-by: Nitesh Narayan Lal >>>> The driver changes are straightforward, but this isn't the only driver >>>> with this issue, right? I'm sure ixgbe and ice both have this problem >>>> too, you should fix them as well, at a minimum, and probably other >>>> vendors drivers: >>>> >>>> $ rg -c --stats num_online_cpus drivers/net/ethernet >>>> ... >>>> 50 files contained matches >>> Ouch, I was indeed surprised that these MSI vector allocations were don= e >>> at the driver level and not at some $SUBSYSTEM level. >>> >>> The logic is already there in the driver so I wouldn't oppose to this v= ery patch >>> but would a shared infrastructure make sense for this? Something that w= ould >>> also handle hotplug operations? >>> >>> Does it possibly go even beyond networking drivers? >> From a generic solution perspective, I think it makes sense to come up w= ith a >> shared infrastructure. >> Something that can be consumed by all the drivers and maybe hotplug oper= ations >> as well (I will have to further explore the hotplug part). > That would be great. I'm completely clueless about those MSI things and t= he > actual needs of those drivers. Now it seems to me that if several CPUs be= come > offline, or as is planned in the future, CPU isolation gets enabled/disab= led > through cpuset, then the vectors may need some reorganization. +1 > > But I don't also want to push toward a complicated solution to handle CPU= hotplug > if there is no actual problem to solve there. Sure, even I am not particularly sure about the hotplug scenarios. > So I let you guys judge. > >> However, there are RT workloads that are getting affected because of thi= s >> issue, so does it make sense to go ahead with this per-driver basis appr= oach >> for now? > Yep that sounds good. Thank you for confirming. > >> Since a generic solution will require a fair amount of testing and >> understanding of different drivers. Having said that, I can definetly st= art >> looking in that direction. > Thanks a lot! > --=20 Nitesh --x5qKUNoegkyIUmDvOHigPup1eCGwUT80c-- --PDZV0yVtrsnz8iCpGtGumojvMZCcYC0xg Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEkXcoRVGaqvbHPuAGo4ZA3AYyozkFAl9p/UoACgkQo4ZA3AYy ozmWsBAAmDk7hoXzvBimZ9o8XOMTtZm4JymymG60f/Y7/vHbueNuCUG7DmI7mBiS VJEpIR4SVvwCt0w3E3WzQAmHRyzYNxIKBkpW3p6RaSbBFhuT9nMSKOzELtiBF7AV o9lfOMjMIiXhVcTKqxhJvIToVC0VaY4FEUvcam7BQG5DO16OCaBOMx6V5nrf5t2F /+YVmD15dryE/rTvYuwi9AZMGXBCMOq9SwxIr2sD7W5/62E0WQH3fyJInQnpLSbK xma8IsQaWKTdck2JBNBdBqssg/CRNSz82oHGLv5Tl/+IzUDu+t+Aody5Toq/TYJg iDidFzqF/mNyqlBxTC8HC++ofuzfPP1UY4wZXB76NoJdbSfDEDwysls55oGsODQl yUz1Ggaa9wul8Te0uYkezbn3pTWmMWBkWtvt7YVE6gbhWcDnr5YpAMx55/ntjl+C x9r7UL6J5jRMkYquRO1fkeo5gFB3wQ3d1VYHG1HNo4tAMvxfwNGoL0XVHdFWx0uD dzlwf8YzTkQVzZjQ8I05XWnm0cf7g2KS3BMBbL7ywUIriV7GGnbCbr0czpfCTeau IyOY7RdCG6MriQPGfsg3pKY/PwFdh4MOWIRXJoQMVR4Mb1JnTeWQQA5LC3RyOJHR Lgy78jBtNjDkGg6s7daYqnvpzRrhcu3Cfo04uePLhMsvX2fLGLg= =OcfM -----END PGP SIGNATURE----- --PDZV0yVtrsnz8iCpGtGumojvMZCcYC0xg--