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Jacob Keller cbd6b3694a i40e/i40evf: spread CPU affinity hints across online CPUs only 
[ Upstream commit be664cbefc ]

Currently, when setting up the IRQ for a q_vector, we set an affinity
hint based on the v_idx of that q_vector. Meaning a loop iterates on
v_idx, which is an incremental value, and the cpumask is created based
on this value.

This is a problem in systems with multiple logical CPUs per core (like in
simultaneous multithreading (SMT) scenarios). If we disable some logical
CPUs, by turning SMT off for example, we will end up with a sparse
cpu_online_mask, i.e., only the first CPU in a core is online, and
incremental filling in q_vector cpumask might lead to multiple offline
CPUs being assigned to q_vectors.

Example: if we have a system with 8 cores each one containing 8 logical
CPUs (SMT == 8 in this case), we have 64 CPUs in total. But if SMT is
disabled, only the 1st CPU in each core remains online, so the
cpu_online_mask in this case would have only 8 bits set, in a sparse way.

In general case, when SMT is off the cpu_online_mask has only C bits set:
0, 1*N, 2*N, ..., C*(N-1)  where
C == # of cores;
N == # of logical CPUs per core.
In our example, only bits 0, 8, 16, 24, 32, 40, 48, 56 would be set.

Instead, we should only assign hints for CPUs which are online. Even
better, the kernel already provides a function, cpumask_local_spread()
which takes an index and returns a CPU, spreading the interrupts across
local NUMA nodes first, and then remote ones if necessary.

Since we generally have a 1:1 mapping between vectors and CPUs, there
is no real advantage to spreading vectors to local CPUs first. In order
to avoid mismatch of the default XPS hints, we'll pass -1 so that it
spreads across all CPUs without regard to the node locality.

Note that we don't need to change the q_vector->affinity_mask as this is
initialized to cpu_possible_mask, until an actual affinity is set and
then notified back to us.

Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2017-12-25 14:26:27 +01:00
arch kvm, mm: account kvm related kmem slabs to kmemcg 2017-12-25 14:26:25 +01:00
block block,bfq: Disable writeback throttling 2017-12-25 14:26:26 +01:00
certs License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
crypto crypto: lrw - Fix an error handling path in 'create()' 2017-12-25 14:26:25 +01:00
Documentation x86/kasan: Use the same shadow offset for 4- and 5-level paging 2017-12-25 14:26:15 +01:00
drivers i40e/i40evf: spread CPU affinity hints across online CPUs only 2017-12-25 14:26:27 +01:00
firmware License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
fs locking/barriers: Convert users of lockless_dereference() to READ_ONCE() 2017-12-25 14:26:21 +01:00
include iio: st_sensors: add register mask for status register 2017-12-25 14:26:26 +01:00
init License cleanup: add SPDX license identifiers to some files 2017-11-02 10:04:46 -07:00
ipc License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
kernel locking/barriers: Convert users of lockless_dereference() to READ_ONCE() 2017-12-25 14:26:21 +01:00
lib x86/unwind: Rename unwinder config options to 'CONFIG_UNWINDER_*' 2017-12-25 14:26:13 +01:00
mm locking/barriers: Convert users of lockless_dereference() to READ_ONCE() 2017-12-25 14:26:21 +01:00
net ipv6: grab rt->rt6i_ref before allocating pcpu rt 2017-12-25 14:26:27 +01:00
samples samples/bpf: adjust rlimit RLIMIT_MEMLOCK for xdp1 2017-12-20 10:10:31 +01:00
scripts x86/unwind: Rename unwinder config options to 'CONFIG_UNWINDER_*' 2017-12-25 14:26:13 +01:00
security apparmor: fix leak of null profile name if profile allocation fails 2017-12-14 09:53:06 +01:00
sound ASoC: rsnd: rsnd_ssi_run_mods() needs to care ssi_parent_mod 2017-12-20 10:10:28 +01:00
tools selftests/x86/ldt_gdt: Run most existing LDT test cases against the GDT as well 2017-12-25 14:26:19 +01:00
usr initramfs: fix initramfs rebuilds w/ compression after disabling 2017-11-03 07:39:19 -07:00
virt kvm, mm: account kvm related kmem slabs to kmemcg 2017-12-25 14:26:25 +01:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support to generate LLVM assembly files 2017-04-25 08:13:52 +09:00
.mailmap .mailmap: Add Maciej W. Rozycki's Imagination e-mail address 2017-11-10 12:16:15 -08:00
COPYING [PATCH] update FSF address in COPYING 2005-09-10 10:06:29 -07:00
CREDITS MAINTAINERS: update TPM driver infrastructure changes 2017-11-09 17:58:40 -08:00
Kbuild License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
Kconfig License cleanup: add SPDX GPL-2.0 license identifier to files with no license 2017-11-02 11:10:55 +01:00
MAINTAINERS Merge branch 'akpm' (patches from Andrew) 2017-11-09 18:26:51 -08:00
Makefile x86/unwind: Rename unwinder config options to 'CONFIG_UNWINDER_*' 2017-12-25 14:26:13 +01:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

README 

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.