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Rik van Riel a04fe3bfc7 x86/mm/tlb: Only trim the mm_cpumask once a second
[ Upstream commit 6db2526c1d ]

Setting and clearing CPU bits in the mm_cpumask is only ever done
by the CPU itself, from the context switch code or the TLB flush
code.

Synchronization is handled by switch_mm_irqs_off() blocking interrupts.

Sending TLB flush IPIs to CPUs that are in the mm_cpumask, but no
longer running the program causes a regression in the will-it-scale
tlbflush2 test. This test is contrived, but a large regression here
might cause a small regression in some real world workload.

Instead of always sending IPIs to CPUs that are in the mm_cpumask,
but no longer running the program, send these IPIs only once a second.

The rest of the time we can skip over CPUs where the loaded_mm is
different from the target mm.

Reported-by: kernel test roboto <oliver.sang@intel.com>
Signed-off-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: https://lore.kernel.org/r/20241204210316.612ee573@fangorn
Closes: https://lore.kernel.org/oe-lkp/202411282207.6bd28eae-lkp@intel.com/
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-02-21 13:57:12 +01:00
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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 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.