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Tue, 20 Oct 2020 14:39:47 +0000 (UTC) Received: from [10.10.115.117] (ovpn-115-117.rdu2.redhat.com [10.10.115.117]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B635855771; Tue, 20 Oct 2020 14:39:40 +0000 (UTC) From: Nitesh Narayan Lal Subject: Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping CPUs To: Peter Zijlstra Cc: Marcelo Tosatti , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-pci@vger.kernel.org, intel-wired-lan@lists.osuosl.org, frederic@kernel.org, sassmann@redhat.com, jesse.brandeburg@intel.com, lihong.yang@intel.com, helgaas@kernel.org, jeffrey.t.kirsher@intel.com, jacob.e.keller@intel.com, jlelli@redhat.com, hch@infradead.org, bhelgaas@google.com, mike.marciniszyn@intel.com, dennis.dalessandro@intel.com, thomas.lendacky@amd.com, jiri@nvidia.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, lgoncalv@redhat.com References: <20200928183529.471328-1-nitesh@redhat.com> <20200928183529.471328-5-nitesh@redhat.com> <20201016122046.GP2611@hirez.programming.kicks-ass.net> <79f382a7-883d-ff42-394d-ec4ce81fed6a@redhat.com> <20201019111137.GL2628@hirez.programming.kicks-ass.net> <20201019140005.GB17287@fuller.cnet> <20201020073055.GY2611@hirez.programming.kicks-ass.net> <078e659e-d151-5bc2-a7dd-fe0070267cb3@redhat.com> <20201020134128.GT2628@hirez.programming.kicks-ass.net> 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: <20201020134128.GT2628@hirez.programming.kicks-ass.net> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 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="Ja5fa0lNIQnbJpPC6unqZMHfvmyf2P2Yc" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --Ja5fa0lNIQnbJpPC6unqZMHfvmyf2P2Yc Content-Type: multipart/mixed; boundary="4cXLyrruUsKXa5wZgbxCmAFIlt5DOlG5Q" --4cXLyrruUsKXa5wZgbxCmAFIlt5DOlG5Q Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US On 10/20/20 9:41 AM, Peter Zijlstra wrote: > On Tue, Oct 20, 2020 at 09:00:01AM -0400, Nitesh Narayan Lal wrote: >> On 10/20/20 3:30 AM, Peter Zijlstra wrote: >>> On Mon, Oct 19, 2020 at 11:00:05AM -0300, Marcelo Tosatti wrote: >>>>> So I think it is important to figure out what that driver really want= s >>>>> in the nohz_full case. If it wants to retain N interrupts per CPU, an= d >>>>> only reduce the number of CPUs, the proposed interface is wrong. >>>> It wants N interrupts per non-isolated (AKA housekeeping) CPU. >>> Then the patch is wrong and the interface needs changing from @min_vecs= , >>> @max_vecs to something that expresses the N*nr_cpus relation. >> Reading Marcelo's comment again I think what is really expected is 1 >> interrupt per non-isolated (housekeeping) CPU (not N interrupts). > Then what is the point of them asking for N*nr_cpus when there is no > isolation? > > Either everybody wants 1 interrupts per CPU and we can do the clamp > unconditionally, in which case we should go fix this user, or they want > multiple per cpu and we should go fix the interface. > > It cannot be both. Based on my understanding I don't think this is consistent, the number of interrupts any driver can request varies to an extent that some consumer of this API even request just one interrupt for its use. This was one of the reasons why I thought of having a conditional restriction. But I agree there is a lack of consistency. --=20 Nitesh --4cXLyrruUsKXa5wZgbxCmAFIlt5DOlG5Q-- --Ja5fa0lNIQnbJpPC6unqZMHfvmyf2P2Yc Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEkXcoRVGaqvbHPuAGo4ZA3AYyozkFAl+O9qsACgkQo4ZA3AYy oznNiA//T1P40BotFV/00IHw14ql/ry4mKi2+1l43JAkn0xcu5PnoQXpJaXcsIO/ wXdMiHmX4gHeaRvAs+SWrN9hh5hU1ItulrSKbF4iu1lOBGn739AI5yrgdBDOvccR mQDQ79vuj794T9NOomdo1PnfbA0dFvTfpSwAx76QYhXyH3OYO4lTjeSZKQ1kswYd 3mUFF3IM0Wh96e2e22L2KwWFhsNkWuJO7V8XlfNPs5qVVMCZ6rYJHRp7rYBaH6Ri ZkLHlAsoEpd+8FNI0EXDkQsEPhNDuTZ93iD4LwkCbpJsXQzpcwlGp/02jbMUDwZG yAWZ1C2XDF3tj9Sd7zXnauBk8CWwFLZnnCoXtsvrbGeleNqevbB1zJxbM1/O/i3p FPqQMv5tlyZDvtCA8kX5kPKZa1rRVPNCE42RHUntxY41qK+ttO6HzAMW3UdLvsBs YxtYB4Ovwa56xL3ezXj87hcoXW2I4Ufhg19uWUsPkMtleXRlOPBwZNcQ2/B1CA6G sMHVVIcuTLJJOtLPEWLILxV3PGcc1zm7mpOrBws24D0SnNrUCSq8tmfBnyjM1w/Y 2sTxeJPw5DlOnFn8b5sUwkPXqIbrdEnXTzh1mbchEyJ9Qh6TbRWh868HKSIL6/OM uG2n7Ci6OVp+vJfs0p+hAVuBXUcRz8Z9ge2nsThMtPreyamxfR0= =9QDL -----END PGP SIGNATURE----- --Ja5fa0lNIQnbJpPC6unqZMHfvmyf2P2Yc-- From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nitesh Narayan Lal Date: Tue, 20 Oct 2020 10:39:38 -0400 Subject: [Intel-wired-lan] [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping CPUs In-Reply-To: <20201020134128.GT2628@hirez.programming.kicks-ass.net> References: <20200928183529.471328-1-nitesh@redhat.com> <20200928183529.471328-5-nitesh@redhat.com> <20201016122046.GP2611@hirez.programming.kicks-ass.net> <79f382a7-883d-ff42-394d-ec4ce81fed6a@redhat.com> <20201019111137.GL2628@hirez.programming.kicks-ass.net> <20201019140005.GB17287@fuller.cnet> <20201020073055.GY2611@hirez.programming.kicks-ass.net> <078e659e-d151-5bc2-a7dd-fe0070267cb3@redhat.com> <20201020134128.GT2628@hirez.programming.kicks-ass.net> Message-ID: <6736e643-d4ae-9919-9ae1-a73d5f31463e@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: intel-wired-lan@osuosl.org List-ID: On 10/20/20 9:41 AM, Peter Zijlstra wrote: > On Tue, Oct 20, 2020 at 09:00:01AM -0400, Nitesh Narayan Lal wrote: >> On 10/20/20 3:30 AM, Peter Zijlstra wrote: >>> On Mon, Oct 19, 2020 at 11:00:05AM -0300, Marcelo Tosatti wrote: >>>>> So I think it is important to figure out what that driver really wants >>>>> in the nohz_full case. If it wants to retain N interrupts per CPU, and >>>>> only reduce the number of CPUs, the proposed interface is wrong. >>>> It wants N interrupts per non-isolated (AKA housekeeping) CPU. >>> Then the patch is wrong and the interface needs changing from @min_vecs, >>> @max_vecs to something that expresses the N*nr_cpus relation. >> Reading Marcelo's comment again I think what is really expected is 1 >> interrupt per non-isolated (housekeeping) CPU (not N interrupts). > Then what is the point of them asking for N*nr_cpus when there is no > isolation? > > Either everybody wants 1 interrupts per CPU and we can do the clamp > unconditionally, in which case we should go fix this user, or they want > multiple per cpu and we should go fix the interface. > > It cannot be both. Based on my understanding I don't think this is consistent, the number of interrupts any driver can request varies to an extent that some consumer of this API even request just one interrupt for its use. This was one of the reasons why I thought of having a conditional restriction. But I agree there is a lack of consistency. -- Nitesh -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 833 bytes Desc: OpenPGP digital signature URL: