Re: Unacceptably Poor RAID1 Performance with Many CPU Cores

[Xiao Ni <xni@redhat.com>]

On Fri, Jun 16, 2023 at 8:27 PM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>
> Hi,
>
> 在 2023/06/16 19:51, Ali Gholami Rudi 写道:
> >
>
> Thanks for testing!
>
> > 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?

Regards
Xiao