Re: [PATCH v2] pipe: use __pipe_{lock,unlock} instead of spinlock

[Hongchen Zhang]

Hi Andrew,
On 2023/1/6 am 10:59, Andrew Morton wrote:
> On Tue,  3 Jan 2023 14:33:03 +0800 Hongchen Zhang <zhanghongchen@xxxxxxxxxxx> wrote:
>
> > Use spinlock in pipe_read/write cost too much time,IMO
> > pipe->{head,tail} can be protected by __pipe_{lock,unlock}.
> > On the other hand, we can use __pipe_lock/unlock to protect the
> > pipe->head/tail in pipe_resize_ring and post_one_notification.
>
> Can you please test this with the test code in Linus's 0ddad21d3e99 and
> check that performance is good?
I tested with the test code in Linus's 0ddad21d3e99,and get the 
following result:

1) before this patch
         13,136.54 msec task-clock           #    3.870 CPUs utilized 

         1,186,779      context-switches     #   90.342 K/sec 

           668,867      cpu-migrations       #   50.917 K/sec 

               895      page-faults          #   68.131 /sec 

    29,875,711,543      cycles               #    2.274 GHz 

    12,372,397,462      instructions         #    0.41  insn per cycle 

     2,480,235,723      branches             #  188.804 M/sec 

        47,191,943      branch-misses        #    1.90% of all branches 


       3.394806886 seconds time elapsed

       0.037869000 seconds user
       0.189346000 seconds sys

2) after this patch

         12,395.63 msec task-clock          #    4.138 CPUs utilized 

         1,193,381      context-switches    #   96.274 K/sec 

           585,543      cpu-migrations      #   47.238 K/sec 

             1,063      page-faults         #   85.756 /sec 

    27,691,587,226      cycles              #    2.234 GHz 

    11,738,307,999      instructions        #    0.42  insn per cycle 

     2,351,299,522      branches            #  189.688 M/sec 

        45,404,526      branch-misses       #    1.93% of all branches 


       2.995280878 seconds time elapsed

       0.010615000 seconds user
       0.206999000 seconds sys
After adding this patch, the time used on this test program becomes less.

Another thing, because of my carelessness, trinity tool tested a bug, I
will remove the unnecessary __pipe_{lock,unlock} in pipe_resize_ring in 
v3, because the lock is owned in pipe_fcntl/pipe_ioctl.

Thanks.