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cb1fa2e999
A multi-thread customer workload with large memory footprint uses fork()/exec() to run some external programs every tens seconds. When running the workload on an arm64 server machine, it's observed that quite some CPU cycles are spent in the TLB flushing functions. While running the workload on the x86_64 server machine, it's not. This causes the performance on arm64 to be much worse than that on x86_64. During the workload running, after fork()/exec() write-protects all pages in the parent process, memory writing in the parent process will cause a write protection fault. Then the page fault handler will make the PTE/PDE writable if the page can be reused, which is almost always true in the workload. On arm64, to avoid the write protection fault on other CPUs, the page fault handler flushes the TLB globally with TLBI broadcast after changing the PTE/PDE. However, this isn't always necessary. Firstly, it's safe to leave some stale read-only TLB entries as long as they will be flushed finally. Secondly, it's quite possible that the original read-only PTE/PDEs aren't cached in remote TLB at all if the memory footprint is large. In fact, on x86_64, the page fault handler doesn't flush the remote TLB in this situation, which benefits the performance a lot. To improve the performance on arm64, make the write protection fault handler flush the TLB locally instead of globally via TLBI broadcast after making the PTE/PDE writable. If there are stale read-only TLB entries in the remote CPUs, the page fault handler on these CPUs will regard the page fault as spurious and flush the stale TLB entries. To test the patchset, make the usemem.c from vm-scalability (https://git.kernel.org/pub/scm/linux/kernel/git/wfg/vm-scalability.git). support calling fork()/exec() periodically. To mimic the behavior of the customer workload, run usemem with 4 threads, access 100GB memory, and call fork()/exec() every 40 seconds. Test results show that with the patchset the score of usemem improves ~40.6%. The cycles% of TLB flush functions reduces from ~50.5% to ~0.3% in perf profile. Signed-off-by: Huang Ying <ying.huang@linux.alibaba.com> Reviewed-by: Ryan Roberts <ryan.roberts@arm.com> Reviewed-by: Barry Song <baohua@kernel.org> Acked-by: Zi Yan <ziy@nvidia.com> Cc: Will Deacon <will@kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: David Hildenbrand <david@redhat.com> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com> Cc: Vlastimil Babka <vbabka@suse.cz> Cc: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Yang Shi <yang@os.amperecomputing.com> Cc: Christoph Lameter (Ampere) <cl@gentwo.org> Cc: Dev Jain <dev.jain@arm.com> Cc: Anshuman Khandual <anshuman.khandual@arm.com> Cc: Kefeng Wang <wangkefeng.wang@huawei.com> Cc: Kevin Brodsky <kevin.brodsky@arm.com> Cc: Yin Fengwei <fengwei_yin@linux.alibaba.com> Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Reviewed-by: David Hildenbrand (Red Hat) <david@kernel.org> Signed-off-by: Catalin Marinas <catalin.marinas@arm.com> |
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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.