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Mon, 19 Oct 2020 14:25:30 +0000 (UTC) Received: from [10.10.115.9] (ovpn-115-9.rdu2.redhat.com [10.10.115.9]) by smtp.corp.redhat.com (Postfix) with ESMTPS id A85425D9EF; Mon, 19 Oct 2020 14:25:15 +0000 (UTC) Subject: Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping CPUs To: Marcelo Tosatti , Peter Zijlstra Cc: 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> 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: <20201019140005.GB17287@fuller.cnet> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 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="tWEQL0MQ6sfQOw0wFm7bzfs6AmDdw7Dc7" Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --tWEQL0MQ6sfQOw0wFm7bzfs6AmDdw7Dc7 Content-Type: multipart/mixed; boundary="dqzUao2zxl46IcY3BVznZvZYz5G7v1wy1" --dqzUao2zxl46IcY3BVznZvZYz5G7v1wy1 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US On 10/19/20 10:00 AM, Marcelo Tosatti wrote: > On Mon, Oct 19, 2020 at 01:11:37PM +0200, Peter Zijlstra wrote: >> On Sun, Oct 18, 2020 at 02:14:46PM -0400, Nitesh Narayan Lal wrote: [...] >>>> Also, do we really need to have that conditional on hk_cpus < >>>> num_online_cpus()? That is, why can't we do this unconditionally? >>> FWIU most of the drivers using this API already restricts the number of >>> vectors based on the num_online_cpus, if we do it unconditionally we ca= n >>> unnecessary duplicate the restriction for cases where we don't have any >>> isolated CPUs. >> unnecessary isn't really a concern here, this is a slow path. What's >> important is code clarity. Right, I can skip that check then. >> >>> Also, different driver seems to take different factors into considerati= on >>> along with num_online_cpus while finding the max_vecs to request, for >>> example in the case of mlx5: >>> MLX5_CAP_GEN(dev, num_ports) * num_online_cpus() + >>> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2= =A0=C2=A0=C2=A0 MLX5_EQ_VEC_COMP_BASE >>> >>> Having hk_cpus < num_online_cpus() helps us ensure that we are only >>> changing the behavior when we have isolated CPUs. >>> >>> Does that make sense? >> That seems to want to allocate N interrupts per cpu (plus some random >> static amount, which seems weird, but whatever). This patch breaks that. > On purpose. For the isolated CPUs we don't want network device=20 > interrupts (in this context). > >> 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. > Zero interrupts for isolated interrupts. Right, otherwise we may end up in a situation where we run out of per CPU vectors while we move the IRQs from isolated CPUs to housekeeping. --=20 Thanks Nitesh --dqzUao2zxl46IcY3BVznZvZYz5G7v1wy1-- --tWEQL0MQ6sfQOw0wFm7bzfs6AmDdw7Dc7 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEkXcoRVGaqvbHPuAGo4ZA3AYyozkFAl+NocoACgkQo4ZA3AYy oznqZg/7Ba39pu3NNBm56g84DMb36tVrJu7NGjL1p/BI+UMF6RMW/6BAK5zLJX0t To4aDzAVptZcfUHW8S5Xqfk94ElvXB8eV65pqd3/iNpATBYQfJhTxz4iTb5/wc6Y uDKrPyCqbBQzzX9MAcO2LRE84q1tmepHsqtXvTGHKXniZA/6R0jtur4fmPiESbwZ MchNGZidx9EMHz3uh3K1RChZtygCjt7zlWjJL/3BAlnNZSatoQ4RJb2jOJ9LsE99 iuv7wXx6CK1bH6YWi7tH3GWzgLIgMO8Tmilhj4mGN25ltKFsLU4s0NI+qn3QaLIZ x2w9oym5FBS6MgPg4j25ClCHW0DMKGvaHts0i2pkQN54L37RqJPdY+xpyISxvb5c c6CC0u3fe0WhCHJMQJoiFVi5KTzNCFEze0gCAzZCGSl88b8VSzABIV6ASCaZb9rN N5KcEIfEcHPohf9d82iwi3w9qg/t3SeIscykei+h4qQfPXtbI4KHUd7E9PoCdryE /w4d3jUZAV4t5LKbBCAZzOUciZufiVBOzxEldgwfcSfOMWqj3ESkzhjgfj2NTHNV mItfwmyOg/p/hbFadCRhvmYl7mtNbX8VF+POHPxb8MnlItt5ZifpEerhHEhuZ4Ur ifigoCEuMCVvs8XgjRiJ2q/cjkJRG5D/3NqxPXoVMPdnyGOi/L0= =mjOW -----END PGP SIGNATURE----- --tWEQL0MQ6sfQOw0wFm7bzfs6AmDdw7Dc7--