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Mon, 12 Oct 2020 17:42:13 +0000 (UTC) Received: from [10.10.116.246] (ovpn-116-246.rdu2.redhat.com [10.10.116.246]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6B87B6EF59; Mon, 12 Oct 2020 17:42:12 +0000 (UTC) Subject: Re: PCI, isolcpus, and irq affinity To: Bjorn Helgaas , Chris Friesen Cc: linux-pci@vger.kernel.org, Christoph Hellwig , Thomas Gleixner References: <20201012165839.GA3732859@bjorn-Precision-5520> From: Nitesh Narayan Lal Autocrypt: addr=nitesh@redhat.com; prefer-encrypt=mutual; keydata= mQINBFl4pQoBEADT/nXR2JOfsCjDgYmE2qonSGjkM1g8S6p9UWD+bf7YEAYYYzZsLtbilFTe z4nL4AV6VJmC7dBIlTi3Mj2eymD/2dkKP6UXlliWkq67feVg1KG+4UIp89lFW7v5Y8Muw3Fm uQbFvxyhN8n3tmhRe+ScWsndSBDxYOZgkbCSIfNPdZrHcnOLfA7xMJZeRCjqUpwhIjxQdFA7 n0s0KZ2cHIsemtBM8b2WXSQG9CjqAJHVkDhrBWKThDRF7k80oiJdEQlTEiVhaEDURXq+2XmG jpCnvRQDb28EJSsQlNEAzwzHMeplddfB0vCg9fRk/kOBMDBtGsTvNT9OYUZD+7jaf0gvBvBB lbKmmMMX7uJB+ejY7bnw6ePNrVPErWyfHzR5WYrIFUtgoR3LigKnw5apzc7UIV9G8uiIcZEn C+QJCK43jgnkPcSmwVPztcrkbC84g1K5v2Dxh9amXKLBA1/i+CAY8JWMTepsFohIFMXNLj+B RJoOcR4HGYXZ6CAJa3Glu3mCmYqHTOKwezJTAvmsCLd3W7WxOGF8BbBjVaPjcZfavOvkin0u DaFvhAmrzN6lL0msY17JCZo046z8oAqkyvEflFbC0S1R/POzehKrzQ1RFRD3/YzzlhmIowkM BpTqNBeHEzQAlIhQuyu1ugmQtfsYYq6FPmWMRfFPes/4JUU/PQARAQABtCVOaXRlc2ggTmFy YXlhbiBMYWwgPG5pbGFsQHJlZGhhdC5jb20+iQI9BBMBCAAnBQJZeKUKAhsjBQkJZgGABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheAAAoJEKOGQNwGMqM56lEP/A2KMs/pu0URcVk/kqVwcBhU SnvB8DP3lDWDnmVrAkFEOnPX7GTbactQ41wF/xwjwmEmTzLrMRZpkqz2y9mV0hWHjqoXbOCS 6RwK3ri5e2ThIPoGxFLt6TrMHgCRwm8YuOSJ97o+uohCTN8pmQ86KMUrDNwMqRkeTRW9wWIQ EdDqW44VwelnyPwcmWHBNNb1Kd8j3xKlHtnS45vc6WuoKxYRBTQOwI/5uFpDZtZ1a5kq9Ak/ MOPDDZpd84rqd+IvgMw5z4a5QlkvOTpScD21G3gjmtTEtyfahltyDK/5i8IaQC3YiXJCrqxE r7/4JMZeOYiKpE9iZMtS90t4wBgbVTqAGH1nE/ifZVAUcCtycD0f3egX9CHe45Ad4fsF3edQ ESa5tZAogiA4Hc/yQpnnf43a3aQ67XPOJXxS0Qptzu4vfF9h7kTKYWSrVesOU3QKYbjEAf95 NewF9FhAlYqYrwIwnuAZ8TdXVDYt7Z3z506//sf6zoRwYIDA8RDqFGRuPMXUsoUnf/KKPrtR ceLcSUP/JCNiYbf1/QtW8S6Ca/4qJFXQHp0knqJPGmwuFHsarSdpvZQ9qpxD3FnuPyo64S2N Dfq8TAeifNp2pAmPY2PAHQ3nOmKgMG8Gn5QiORvMUGzSz8Lo31LW58NdBKbh6bci5+t/HE0H pnyVf5xhNC/FuQINBFl4pQoBEACr+MgxWHUP76oNNYjRiNDhaIVtnPRqxiZ9v4H5FPxJy9UD Bqr54rifr1E+K+yYNPt/Po43vVL2cAyfyI/LVLlhiY4yH6T1n+Di/hSkkviCaf13gczuvgz4 KVYLwojU8+naJUsiCJw01MjO3pg9GQ+47HgsnRjCdNmmHiUQqksMIfd8k3reO9SUNlEmDDNB XuSzkHjE5y/R/6p8uXaVpiKPfHoULjNRWaFc3d2JGmxJpBdpYnajoz61m7XJlgwl/B5Ql/6B dHGaX3VHxOZsfRfugwYF9CkrPbyO5PK7yJ5vaiWre7aQ9bmCtXAomvF1q3/qRwZp77k6i9R3 tWfXjZDOQokw0u6d6DYJ0Vkfcwheg2i/Mf/epQl7Pf846G3PgSnyVK6cRwerBl5a68w7xqVU 4KgAh0DePjtDcbcXsKRT9D63cfyfrNE+ea4i0SVik6+N4nAj1HbzWHTk2KIxTsJXypibOKFX 2VykltxutR1sUfZBYMkfU4PogE7NjVEU7KtuCOSAkYzIWrZNEQrxYkxHLJsWruhSYNRsqVBy KvY6JAsq/i5yhVd5JKKU8wIOgSwC9P6mXYRgwPyfg15GZpnw+Fpey4bCDkT5fMOaCcS+vSU1 UaFmC4Ogzpe2BW2DOaPU5Ik99zUFNn6cRmOOXArrryjFlLT5oSOe4IposgWzdwARAQABiQIl BBgBCAAPBQJZeKUKAhsMBQkJZgGAAAoJEKOGQNwGMqM5ELoP/jj9d9gF1Al4+9bngUlYohYu 0sxyZo9IZ7Yb7cHuJzOMqfgoP4tydP4QCuyd9Q2OHHL5AL4VFNb8SvqAxxYSPuDJTI3JZwI7 d8JTPKwpulMSUaJE8ZH9n8A/+sdC3CAD4QafVBcCcbFe1jifHmQRdDrvHV9Es14QVAOTZhnJ vweENyHEIxkpLsyUUDuVypIo6y/Cws+EBCWt27BJi9GH/EOTB0wb+2ghCs/i3h8a+bi+bS7L FCCm/AxIqxRurh2UySn0P/2+2eZvneJ1/uTgfxnjeSlwQJ1BWzMAdAHQO1/lnbyZgEZEtUZJ x9d9ASekTtJjBMKJXAw7GbB2dAA/QmbA+Q+Xuamzm/1imigz6L6sOt2n/X/SSc33w8RJUyor SvAIoG/zU2Y76pKTgbpQqMDmkmNYFMLcAukpvC4ki3Sf086TdMgkjqtnpTkEElMSFJC8npXv 3QnGGOIfFug/qs8z03DLPBz9VYS26jiiN7QIJVpeeEdN/LKnaz5LO+h5kNAyj44qdF2T2AiF HxnZnxO5JNP5uISQH3FjxxGxJkdJ8jKzZV7aT37sC+Rp0o3KNc+GXTR+GSVq87Xfuhx0LRST NK9ZhT0+qkiN7npFLtNtbzwqaqceq3XhafmCiw8xrtzCnlB/C4SiBr/93Ip4kihXJ0EuHSLn VujM7c/b4pps Organization: Red Hat Inc, Message-ID: Date: Mon, 12 Oct 2020 13:42:11 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20201012165839.GA3732859@bjorn-Precision-5520> 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="MaJAC7c47IgYkkRTfjhpwEgxbf5hUPD6V" Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --MaJAC7c47IgYkkRTfjhpwEgxbf5hUPD6V Content-Type: multipart/mixed; boundary="rqW7QCfBLATHiRUavwbNUyQ7NFh3HNrrr" --rqW7QCfBLATHiRUavwbNUyQ7NFh3HNrrr Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US On 10/12/20 12:58 PM, Bjorn Helgaas wrote: > [+cc Christoph, Thomas, Nitesh] > > On Mon, Oct 12, 2020 at 09:49:37AM -0600, Chris Friesen wrote: >> I've got a linux system running the RT kernel with threaded irqs.=C2=A0 = On >> startup we affine the various irq threads to the housekeeping CPUs, but = I >> recently hit a scenario where after some days of uptime we ended up with= a >> number of NVME irq threads affined to application cores instead (not goo= d >> when we're trying to run low-latency applications). > pci_alloc_irq_vectors_affinity() basically just passes affinity > information through to kernel/irq/affinity.c, and the PCI core doesn't > change affinity after that. > >> Looking at the code, it appears that the NVME driver can in some scenari= os >> end up calling pci_alloc_irq_vectors_affinity() after initial system >> startup, which seems to determine CPU affinity without any regard for th= ings >> like "isolcpus" or "cset shield". >> >> There seem to be other reports of similar issues: >> >> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1831566 >> >> It looks like some SCSI drivers and virtio_pci_common.c will also call >> pci_alloc_irq_vectors_affinity(), though I'm not sure if they would ever= do >> it after system startup. >> >> How does it make sense for the PCI subsystem to affine interrupts to CPU= s >> which have explicitly been designated as "isolated"? > This recent thread may be useful: > > https://lore.kernel.org/linux-pci/20200928183529.471328-1-nitesh@redhat= .com/ > > It contains a patch to "Limit pci_alloc_irq_vectors() to housekeeping > CPUs". I'm not sure that patch summary is 100% accurate because IIUC > that particular patch only reduces the *number* of vectors allocated > and does not actually *limit* them to housekeeping CPUs. That is correct the above-mentioned patch is just to reduce the number of vectors. Based on the problem that has been described here, I think the issue could be the usage of cpu_online_mask/cpu_possible_mask while creating the affinity mask or while distributing the jobs. What we should be doing in these cases is to basically use the housekeeping_cpumask instead. A few months back similar issue has been fixed for cpumask_local_spread and some other sub-systems [1]. [1] https://lore.kernel.org/lkml/20200625223443.2684-1-nitesh@redhat.com/ --=20 Nitesh --rqW7QCfBLATHiRUavwbNUyQ7NFh3HNrrr-- --MaJAC7c47IgYkkRTfjhpwEgxbf5hUPD6V Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEEkXcoRVGaqvbHPuAGo4ZA3AYyozkFAl+ElXMACgkQo4ZA3AYy ozm6pA//Rf/OmO3IFCzF/UNjGgaNdf5tNyN6iPoU76O0sOCEnlde11rmnu7R2X0d uLo0gF+yqmuq1HyBDUyp9EjQ6AEu8JBzkmAJWVZnwktEwbtaCF4ZYc2XThp5rRR0 wARqZHn8yua0kmZGQaCA/EmvEYtMlB1Z2aIP948E1bS4lcLl1m+khuUx+DbEBywL OiWMDTblSJ+RVnSbPaCNdYvCtKsD5xoU4H/5RT9CsPirbzcaF9bteq2xAEXcUjow fQIc5bMJEcNb6QuVDodAfBh7qMTZyV2bqJg361zVz1ixYHiTbxseqmqKa95UrDXF vnabob8XCNC1zfcPAGaSMb3r2VA830OSJorz4MyYrSHW0rIOxchhzCcAstPT/ByF cwGK3ub5wVD9jm0gKVGucYwERFA4r1+/ekEnSrWDGmnS+B1BaxQCluOJuHx6E7kh IChSASx7h9uD3zPAVHKIJfEm0kQN91ZPvfpqLYBXMohqqwLFpW/BfGfFxGGu3V4a OurV3pWSNL6Icu9xza6K1zJp8BECpmQ1fmdMR2mxxQ/U+OJ1b85Ml8sC7bmvRiWP vq+iyy5vsQU2JQO/UXvuFSjfffDhQz1xYGq9/7dcyULN07dYp2rXsPUYDoXMklfT yre/iTMrEsTCqmRfpbvQhaH1ClJEjRIfdnNLoG1PsNV4ZpT5F0E= =Rliz -----END PGP SIGNATURE----- --MaJAC7c47IgYkkRTfjhpwEgxbf5hUPD6V--