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refresh_zone_stat_thresholds function has two loops which is expensive for higher number of CPUs and NUMA nodes. Below is the rough estimation of total iterations done by these loops based on number of NUMA and CPUs. Total number of iterations: nCPU * 2 * Numa * mCPU Where: nCPU = total number of CPUs Numa = total number of NUMA nodes mCPU = mean value of total CPUs (e.g., 512 for 1024 total CPUs) For the system under test with 16 NUMA nodes and 1024 CPUs, this results in a substantial increase in the number of loop iterations during boot-up when NUMA is enabled: No NUMA = 1024*2*1*512 = 1,048,576 : Here refresh_zone_stat_thresholds takes around 224 ms total for all the CPUs in the system under test. 16 NUMA = 1024*2*16*512 = 16,777,216 : Here refresh_zone_stat_thresholds takes around 4.5 seconds total for all the CPUs in the system under test. Calling this for each CPU is expensive when there are large number of CPUs along with multiple NUMAs. Fix this by deferring refresh_zone_stat_thresholds to be called later at once when all the secondary CPUs are up. Also, register the DYN hooks to keep the existing hotplug functionality intact. Link: https://lkml.kernel.org/r/1723443220-20623-1-git-send-email-ssengar@linux.microsoft.com Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com> Acked-by: Christoph Lameter <cl@linux.com> Reviewed-by: Srivatsa S. Bhat (Microsoft) <srivatsa@csail.mit.edu> Cc: Saurabh Singh Sengar <ssengar@microsoft.com> Cc: Wei Liu <wei.liu@kernel.org> Cc: Mel Gorman <mgorman@techsingularity.net> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
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.