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Fri, 25 Sep 2020 21:38:14 +0000 (UTC) Received: from [10.10.114.192] (ovpn-114-192.rdu2.redhat.com [10.10.114.192]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C07D75577A; Fri, 25 Sep 2020 21:38:06 +0000 (UTC) Subject: Re: [PATCH v3 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping CPUs To: Bjorn Helgaas Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-pci@vger.kernel.org, intel-wired-lan@lists.osuosl.org, frederic@kernel.org, mtosatti@redhat.com, sassmann@redhat.com, jesse.brandeburg@intel.com, lihong.yang@intel.com, 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, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, lgoncalv@redhat.com References: <20200925202307.GA2456332@bjorn-Precision-5520> From: Nitesh Narayan Lal Autocrypt: addr=nitesh@redhat.com; prefer-encrypt=mutual; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200925202307.GA2456332@bjorn-Precision-5520> 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="YGhoGpiEK97LlikE5tgeBsj6NKFwnYVHR" Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --YGhoGpiEK97LlikE5tgeBsj6NKFwnYVHR Content-Type: multipart/mixed; boundary="Df7GsTEDJLdhut9BI6tcE476jLN1S7Yy0" --Df7GsTEDJLdhut9BI6tcE476jLN1S7Yy0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US On 9/25/20 4:23 PM, Bjorn Helgaas wrote: > On Fri, Sep 25, 2020 at 02:26:54PM -0400, Nitesh Narayan Lal wrote: >> If we have isolated CPUs dedicated for use by real-time tasks, we try to >> move IRQs to housekeeping CPUs from the userspace to reduce latency >> overhead on the isolated CPUs. >> >> If we allocate too many IRQ vectors, moving them all to housekeeping CPU= s >> may exceed per-CPU vector limits. >> >> When we have isolated CPUs, limit the number of vectors allocated by >> pci_alloc_irq_vectors() to the minimum number required by the driver, or >> to one per housekeeping CPU if that is larger. >> >> Signed-off-by: Nitesh Narayan Lal >> --- >> include/linux/pci.h | 17 +++++++++++++++++ >> 1 file changed, 17 insertions(+) >> >> diff --git a/include/linux/pci.h b/include/linux/pci.h >> index 835530605c0d..a7b10240b778 100644 >> --- a/include/linux/pci.h >> +++ b/include/linux/pci.h >> @@ -38,6 +38,7 @@ >> #include >> #include >> #include >> +#include >> #include >> =20 >> #include >> @@ -1797,6 +1798,22 @@ static inline int >> pci_alloc_irq_vectors(struct pci_dev *dev, unsigned int min_vecs, >> =09=09 unsigned int max_vecs, unsigned int flags) >> { >> +=09unsigned int hk_cpus; >> + >> +=09hk_cpus =3D housekeeping_num_online_cpus(HK_FLAG_MANAGED_IRQ); > Add blank line here before the block comment. > >> +=09/* >> +=09 * If we have isolated CPUs for use by real-time tasks, to keep the >> +=09 * latency overhead to a minimum, device-specific IRQ vectors are mo= ved >> +=09 * to the housekeeping CPUs from the userspace by changing their >> +=09 * affinity mask. Limit the vector usage to keep housekeeping CPUs f= rom >> +=09 * running out of IRQ vectors. >> +=09 */ >> +=09if (hk_cpus < num_online_cpus()) { >> +=09=09if (hk_cpus < min_vecs) >> +=09=09=09max_vecs =3D min_vecs; >> +=09=09else if (hk_cpus < max_vecs) >> +=09=09=09max_vecs =3D hk_cpus; >> +=09} > It seems like you'd want to do this inside > pci_alloc_irq_vectors_affinity() since that's an exported interface, > and drivers that use it will bypass the limiting you're doing here. Good point, few drivers directly use this. I took a quick look and it seems I may also have to take the pre and the post vectors into consideration. >> =09return pci_alloc_irq_vectors_affinity(dev, min_vecs, max_vecs, flags= , >> =09=09=09=09=09 NULL); >> } >> --=20 >> 2.18.2 >> --=20 Nitesh --Df7GsTEDJLdhut9BI6tcE476jLN1S7Yy0-- --YGhoGpiEK97LlikE5tgeBsj6NKFwnYVHR Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEkXcoRVGaqvbHPuAGo4ZA3AYyozkFAl9uYz0ACgkQo4ZA3AYy ozkiEBAAvGh1LoOrI92FwWB9mO6IUhqq1kV5fqaTQoQVDCd9xBSPfsWT+gsFaduP L9udE6raj+9EpQkKdIiqcAL5Csx/8KmvNqbeY/ABw4MAlNxlcc9iBHl3dTvkAw9b pPeMsNnQiPPt18S/SYvkUsSVD7tb8S334qRmxQqU2RgjzIX9DZINMbXVhrzbCTkJ gTjsuFAIZyKjw6pHvqc51qWOr91TdMtk3kFyPKSEK5jUGuI36Gmuh38W5o6ZtPuZ 1t9VKvcCODdQE5ehdGN10E7Z0bjDdCkNy+qV3ddgteMr1AHctofL9FbhrAkAIreP BZxJ9YuFkexkNbAJfUIiItFeQMJ8bEhtqz5kuGuod73HjyNsjXrYWy4sCNSizeBN QuoMzNgXPNkp++V6Qv1ta36A+pDM/k0A/W0yC91lPhrhJoV/nWClMayOrk2ywINv H8FtM+Ci0lA6NTVtwDgPVkBe06xgTEENtXQ4EnBxahmJ9DBWDh1N7f1P0J7KYMCB iwxdkktbb0GcVo7/9oOObfztqO/bEat0Nz3pDhJz0XbnhVHCxDeHwtaMgWO/64UJ f6X0MJRX9006GFx7Y2iExMzsyKypT0/+49RXOsFkLMXJidNzylG1OjZw7dtg3z5i Bp9SpF9tRQ3laz3BnyqBuyDbT9EBm4zaUFiQG1ZAv0KqAkAOXVs= =EFzi -----END PGP SIGNATURE----- --YGhoGpiEK97LlikE5tgeBsj6NKFwnYVHR--