Re: [PATCH for-next 4/4] block/rnbd: Remove all likely and unlikely

[Gioh Kim <gi-oh.kim@ionos.com>]

On Thu, Apr 29, 2021 at 9:14 AM Gioh Kim <gi-oh.kim@ionos.com> wrote:
>
> On Wed, Apr 28, 2021 at 8:33 PM Chaitanya Kulkarni
> <Chaitanya.Kulkarni@wdc.com> wrote:
> >
> > On 4/27/21 23:14, Gioh Kim wrote:
> > > The IO performance test with fio after removing the likely and
> > > unlikely macros in all if-statement shows no performance drop.
> > > They do not help for the performance of rnbd.
> > >
> > > The fio test did random read on 32 rnbd devices and 64 processes.
> > > Test environment:
> > > - AMD Opteron(tm) Processor 6386 SE
> > > - 125G memory
> > > - kernel version: 5.4.86
> >
> > why 5.4 and not linux-block/for-next ?
>
> We have done porting only 5.4 for the server machine yet.
>
> >
> > > - gcc version: gcc (Debian 8.3.0-6) 8.3.0
> > > - Infiniband controller: InfiniBand: Mellanox Technologies MT26428
> > > [ConnectX VPI PCIe 2.0 5GT/s - IB QDR / 10GigE] (rev b0)
> > >
> > > before
> > > read: IOPS=549k, BW=2146MiB/s
> > > read: IOPS=544k, BW=2125MiB/s
> > > read: IOPS=553k, BW=2158MiB/s
> > > read: IOPS=535k, BW=2089MiB/s
> > > read: IOPS=543k, BW=2122MiB/s
> > > read: IOPS=552k, BW=2154MiB/s
> > > average: IOPS=546k, BW=2132MiB/s
> > >
> > > after
> > > read: IOPS=556k, BW=2172MiB/s
> > > read: IOPS=561k, BW=2191MiB/s
> > > read: IOPS=552k, BW=2156MiB/s
> > > read: IOPS=551k, BW=2154MiB/s
> > > read: IOPS=562k, BW=2194MiB/s
> > > -----------
> > > average: IOPS=556k, BW=2173MiB/s
> > >
> > > The IOPS and bandwidth got better slightly after removing
> > > likely/unlikely. (IOPS= +1.8% BW= +1.9%) But we cannot make sure
> > > that removing the likely/unlikely help the performance because it
> > > depends on various situations. We only make sure that removing the
> > > likely/unlikely does not drop the performance.
> >
> > Did you get a chance to collect perf numbers to see which functions are
> > getting faster ?

Hi Chaitanya,

I ran the perf tool to find out which functions are getting faster.
But I was not able to find it.
Could you please suggest a tool or anything to check it out?

For your information, below is what I got with 'perf record fio
<options:8-device, 64-job, 60-second>'
The result before/after removing likely/unlikely looks the same.

     4.15%  fio      [kernel.kallsyms]    [k] _raw_spin_lock_irqsave
     3.19%  fio      [kernel.kallsyms]    [k] x86_pmu_disable_all
     2.98%  fio      [rnbd_client]        [k] rnbd_put_permit
     2.77%  fio      [kernel.kallsyms]    [k] find_first_zero_bit
     2.49%  fio      [kernel.kallsyms]    [k] __x86_indirect_thunk_rax
     2.21%  fio      [kernel.kallsyms]    [k] psi_task_change
     2.00%  fio      [kernel.kallsyms]    [k] gup_pgd_range
     1.83%  fio      fio                  [.] 0x0000000000029048
     1.78%  fio      [rnbd_client]        [k] rnbd_get_permit
     1.78%  fio      fio                  [.] axmap_isset
     1.63%  fio      [kernel.kallsyms]    [k] _raw_spin_lock
     1.58%  fio      fio                  [.] fio_gettime
     1.53%  fio      [rtrs_client]        [k] __rtrs_get_permit
     1.51%  fio      [rnbd_client]        [k] rnbd_queue_rq
     1.51%  fio      [rtrs_client]        [k] rtrs_clt_put_permit
     1.47%  fio      [kernel.kallsyms]    [k] try_to_wake_up
     1.31%  fio      [kernel.kallsyms]    [k] kmem_cache_alloc
     1.22%  fio      libc-2.28.so         [.] 0x00000000000a2547
     1.17%  fio      [mlx4_ib]            [k] _mlx4_ib_post_send
     1.14%  fio      [kernel.kallsyms]    [k] blkdev_direct_IO
     1.14%  fio      [kernel.kallsyms]    [k] read_tsc
     1.02%  fio      [rtrs_client]        [k] rtrs_clt_read_req
     0.92%  fio      [rtrs_client]        [k] get_next_path_min_inflight
     0.92%  fio      [kernel.kallsyms]    [k] sched_clock
     0.91%  fio      [kernel.kallsyms]    [k] blk_mq_get_request
     0.87%  fio      [kernel.kallsyms]    [k] x86_pmu_enable_all
     0.87%  fio      [kernel.kallsyms]    [k] __sched_text_start
     0.84%  fio      [kernel.kallsyms]    [k] insert_work
     0.82%  fio      [kernel.kallsyms]    [k] copy_user_generic_string
     0.80%  fio      [kernel.kallsyms]    [k] blk_attempt_plug_merge
     0.73%  fio      [rtrs_client]        [k] rtrs_clt_update_all_stats


>
> I knew somebody would ask for it ;-)
> No, I didn't because I have been occupied with another task.
> But I will check it soon in a few weeks.
>
> Thank you for the review.
>
> >
> >