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From:   Stephen Hemminger <sthemmin@microsoft.com>
To:     "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        Saurabh Sengar <ssengar@linux.microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        Dexuan Cui <decui@microsoft.com>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Saurabh Singh Sengar <ssengar@microsoft.com>
Subject: RE: [PATCH v2] Drivers: hv: vmbus: Don't assign VMbus channel
 interrupts to isolated CPUs
Thread-Topic: [PATCH v2] Drivers: hv: vmbus: Don't assign VMbus channel
 interrupts to isolated CPUs
Thread-Index: AQHYcZqCuyoQmicyPkmbcJqVfL10360y3SZQgAFkOoCAADTLYA==
Date:   Sat, 28 May 2022 16:07:35 +0000
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Doing this will actually help DPDK applications on isolated cpus.
The history is isolated cpus came  first, then cpusets and now the preferre=
d kernel solution is cgroups.

For PCI hardware this is handled in userspace typically since it is a polic=
y decision.

-----Original Message-----
From: Michael Kelley (LINUX) <mikelley@microsoft.com>=20
Sent: Saturday, May 28, 2022 5:56 AM
To: Stephen Hemminger <sthemmin@microsoft.com>; Saurabh Sengar <ssengar@lin=
ux.microsoft.com>; KY Srinivasan <kys@microsoft.com>; Haiyang Zhang <haiyan=
gz@microsoft.com>; wei.liu@kernel.org; Dexuan Cui <decui@microsoft.com>; li=
nux-hyperv@vger.kernel.org; linux-kernel@vger.kernel.org; Saurabh Singh Sen=
gar <ssengar@microsoft.com>
Subject: RE: [PATCH v2] Drivers: hv: vmbus: Don't assign VMbus channel inte=
rrupts to isolated CPUs

From: Stephen Hemminger <sthemmin@microsoft.com> Sent: Friday, May 27, 2022=
 8:41 AM
>=20
> Would this have impact for DPDK applications using isolated cpus?

I don't have any existing knowledge of DPDK use of isolated CPUs,
so someone with more expertise feel free to correct me.

From what I see in the DPDK documentation (Section 8.3 here:
https://nam06.safelinks.protection.outlook.com/?url=3Dhttps%3A%2F%2Fdoc.dpd=
k.org%2Fguides%2Flinux_gsg%2Fenable_func.html&amp;data=3D05%7C01%7Csthemmin=
%40microsoft.com%7C45f1aefca73845a7470408da40a96d81%7C72f988bf86f141af91ab2=
d7cd011db47%7C1%7C0%7C637893393679306569%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC=
4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&am=
p;sdata=3DvT3keyehM9AWGhPJ9ItWJhhjN%2Bl7ZGB07l1KapOG0I0%3D&amp;reserved=3D0=
), there's
no impact.  The example in that documentation does CPU isolation
only for the purpose of scheduling, not for interrupts.  The
example kernel command line is:

isolcpus=3D2,4,6

which defaults to "domain" as the "flag" and is equivalent to:

isolcpus=3Ddomain,2,4,6.

VMbus channel interrupts are affected only if "managed_irq" is
specified as the flag per the commit message below.

And FWIW, cpusets provide a better way to doing scheduler
isolation than the isolcpus kernel boot option.  Perhaps the
DPDK documentation should be updated. :-)

Michael