Re: Unacceptably Poor RAID1 Performance with Many CPU Cores

Hi,

在 2023/06/21 16:05, Xiao Ni 写道:

On Fri, Jun 16, 2023 at 8:27 PM Yu Kuai [off-list ref] wrote:

quoted

Hi,

在 2023/06/16 19:51, Ali Gholami Rudi 写道:

quoted

Thanks for testing!

quoted

Perf's output:

+   93.79%     0.09%  fio      [kernel.kallsyms]       [k] entry_SYSCALL_64_after_hwframe
+   92.89%     0.05%  fio      [kernel.kallsyms]       [k] do_syscall_64
+   86.59%     0.07%  fio      [kernel.kallsyms]       [k] __x64_sys_io_submit
-   85.61%     0.10%  fio      [kernel.kallsyms]       [k] io_submit_one
     - 85.51% io_submit_one
        - 47.98% aio_read
           - 46.18% blkdev_read_iter
              - 44.90% __blkdev_direct_IO_async
                 - 41.68% submit_bio_noacct_nocheck
                    - 41.50% __submit_bio
                       - 18.76% md_handle_request
                          - 18.71% raid10_make_request
                             - 18.54% raid10_read_request
                                  16.54% read_balance

There is not any spin_lock in fast path anymore. Now, looks like
main cost is raid10 io path now(read_balance looks worth
investigation, 16.54% is too much), and for a real device with ms
io latency, I think latency in io path may not matter.

Hi Kuai

Cool. And I noticed you mentioned 'fast path' in many places. What's
the meaning of 'fast path'? Does it mean the path that i/os are
submitting?

Yes, and fast path means the case all resources is available and io can
be submitted to device without blocking.

There should be no spin_lock or atomic ops in fast path, otherwise io
performance will be affected.

Thanks,
Kuai

Regards
Xiao


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