mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2025-01-18 10:56:14 +00:00
22165f61d0
Chen Yu reports a hackbench regression of cluster wakeup when hackbench threads equal to the CPU number [1]. Analysis shows it's because we wake up more on the target CPU even if the prev_cpu is a good wakeup candidate and leads to the decrease of the CPU utilization. Generally if the task's prev_cpu is idle we'll wake up the task on it without scanning. On cluster machines we'll try to wake up the task in the same cluster of the target for better cache affinity, so if the prev_cpu is idle but not sharing the same cluster with the target we'll still try to find an idle CPU within the cluster. This will improve the performance at low loads on cluster machines. But in the issue above, if the prev_cpu is idle but not in the cluster with the target CPU, we'll try to scan an idle one in the cluster. But since the system is busy, we're likely to fail the scanning and use target instead, even if the prev_cpu is idle. Then leads to the regression. This patch solves this in 2 steps: o record the prev_cpu/recent_used_cpu if they're good wakeup candidates but not sharing the cluster with the target. o on scanning failure use the prev_cpu/recent_used_cpu if they're recorded as idle [1] https://lore.kernel.org/all/ZGzDLuVaHR1PAYDt@chenyu5-mobl1/ Closes: https://lore.kernel.org/all/ZGsLy83wPIpamy6x@chenyu5-mobl1/ Reported-by: Chen Yu <yu.c.chen@intel.com> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com> Tested-and-reviewed-by: Chen Yu <yu.c.chen@intel.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org> Link: https://lkml.kernel.org/r/20231019033323.54147-4-yangyicong@huawei.com
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 Restructured Text 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.