Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <a73761e4-b791-e9a2-a276-e1551628e33b@efficios.com>
Date:   Wed, 21 Jun 2023 14:51:42 -0400
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.12.0
Subject: Re: [tip: sched/core] sched: Fix performance regression introduced by
 mm_cid
Content-Language: en-US
To:     Swapnil Sapkal <Swapnil.Sapkal@amd.com>,
        Peter Zijlstra <peterz@infradead.org>
Cc:     linux-kernel@vger.kernel.org, linux-tip-commits@vger.kernel.org,
        Aaron Lu <aaron.lu@intel.com>, x86@kernel.org,
        Andrew Morton <akpm@linux-foundation.org>
References: <168214940343.404.10896712987516429042.tip-bot2@tip-bot2>
 <09e0f469-a3f7-62ef-75a1-e64cec2dcfc5@amd.com>
 <20230620091139.GZ4253@hirez.programming.kicks-ass.net>
 <44428f1e-ca2c-466f-952f-d5ad33f12073@amd.com>
 <3e9eaed6-4708-9e58-c80d-143760d6b23a@efficios.com>
 <ddbd1564-8135-5bc3-72b4-afb7c6e9caba@amd.com>
From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
In-Reply-To: <ddbd1564-8135-5bc3-72b4-afb7c6e9caba@amd.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit
Precedence: bulk

On 6/21/23 12:36, Swapnil Sapkal wrote:
> Hello Mathieu,
> 
[...]
>>
>> I suspect the regression is caused by the mm_count cache line bouncing.
>>
>> Please try with this additional patch applied:
>>
>> https://lore.kernel.org/lkml/20230515143536.114960-1-mathieu.desnoyers@efficios.com/
> 
> Thanks for the suggestion. I tried out with the patch you suggested. I 
> am seeing
> improvement in hackbench numbers with mm_count padding. But this is not 
> matching
> with what we achieved through reverting the new mm_cid patch.
> 
> Below are the results on the 1 Socket 4th Generation EPYC Processor (1 x 
> 96C/192T):
> 
> Threads:
> 
> Test:              Base (v6.4-rc1)   Base + new_mmcid_reverted  Base + 
> mm_count_padding
>   1-groups:         5.23 (0.00 pct)         4.61 (11.85 pct)        5.11 
> (2.29 pct)
>   2-groups:         4.99 (0.00 pct)         4.72 (5.41 pct)         5.00 
> (-0.20 pct)
>   4-groups:         5.96 (0.00 pct)         4.87 (18.28 pct)        5.86 
> (1.67 pct)
>   8-groups:         6.58 (0.00 pct)         5.44 (17.32 pct)        6.20 
> (5.77 pct)
> 16-groups:        11.48 (0.00 pct)         8.07 (29.70 pct)       10.68 
> (6.96 pct)
> 
> Processes:
> 
> Test:              Base (v6.4-rc1)  Base + new_mmcid_reverted   Base + 
> mm_count_padding
>   1-groups:         5.19 (0.00 pct)         4.90 (5.58 pct)         5.19 
> (0.00 pct)
>   2-groups:         5.44 (0.00 pct)         5.39 (0.91 pct)         5.39 
> (0.91 pct)
>   4-groups:         5.69 (0.00 pct)         5.64 (0.87 pct)         5.64 
> (0.87 pct)
>   8-groups:         6.08 (0.00 pct)         6.01 (1.15 pct)         6.04 
> (0.65 pct)
> 16-groups:        10.87 (0.00 pct)        10.83 (0.36 pct)        10.93 
> (-0.55 pct)
> 
> The ibs profile shows that function __switch_to_asm() is coming at top 
> in baseline
> run and is not seen with mm_count padding patch. Will be attaching full 
> ibs profile
> data for all the 3 runs:
> 
> # Base (v6.4-rc1)
> Threads:
> Total time: 11.486 [sec]
> 
>     5.15%  sched-messaging  [kernel.vmlinux]      [k] __switch_to_asm
>     4.31%  sched-messaging  [kernel.vmlinux]      [k] copyout
>     4.29%  sched-messaging  [kernel.vmlinux]      [k] 
> native_queued_spin_lock_slowpath
>     4.22%  sched-messaging  [kernel.vmlinux]      [k] copyin
>     3.92%  sched-messaging  [kernel.vmlinux]      [k] 
> apparmor_file_permission
>     2.91%  sched-messaging  [kernel.vmlinux]      [k] __schedule
>     2.34%  swapper          [kernel.vmlinux]      [k] __switch_to_asm
>     2.10%  sched-messaging  [kernel.vmlinux]      [k] prepare_to_wait_event
>     2.10%  sched-messaging  [kernel.vmlinux]      [k] try_to_wake_up
>     2.07%  sched-messaging  [kernel.vmlinux]      [k] 
> finish_task_switch.isra.0
>     2.00%  sched-messaging  [kernel.vmlinux]      [k] pipe_write
>     1.82%  sched-messaging  [kernel.vmlinux]      [k] 
> check_preemption_disabled
>     1.73%  sched-messaging  [kernel.vmlinux]      [k] 
> exit_to_user_mode_prepare
>     1.52%  sched-messaging  [kernel.vmlinux]      [k] __entry_text_start
>     1.49%  sched-messaging  [kernel.vmlinux]      [k] osq_lock
>     1.45%  sched-messaging  libc.so.6             [.] write
>     1.44%  swapper          [kernel.vmlinux]      [k] native_sched_clock
>     1.38%  sched-messaging  [kernel.vmlinux]      [k] psi_group_change
>     1.38%  sched-messaging  [kernel.vmlinux]      [k] pipe_read
>     1.37%  sched-messaging  libc.so.6             [.] read
>     1.06%  sched-messaging  [kernel.vmlinux]      [k] vfs_read
>     1.01%  swapper          [kernel.vmlinux]      [k] psi_group_change
>     1.00%  sched-messaging  [kernel.vmlinux]      [k] update_curr
> 
> # Base + mm_count_padding
> Threads:
> Total time: 11.384 [sec]
> 
>     4.43%  sched-messaging  [kernel.vmlinux]         [k] copyin
>     4.39%  sched-messaging  [kernel.vmlinux]         [k] 
> native_queued_spin_lock_slowpath
>     4.07%  sched-messaging  [kernel.vmlinux]         [k] 
> apparmor_file_permission
>     4.07%  sched-messaging  [kernel.vmlinux]         [k] copyout
>     2.49%  sched-messaging  [kernel.vmlinux]         [k] entry_SYSCALL_64
>     2.37%  sched-messaging  [kernel.vmlinux]         [k] update_cfs_group
>     2.19%  sched-messaging  [kernel.vmlinux]         [k] pipe_write
>     2.00%  sched-messaging  [kernel.vmlinux]         [k] 
> check_preemption_disabled
>     1.93%  swapper          [kernel.vmlinux]         [k] update_load_avg
>     1.81%  sched-messaging  [kernel.vmlinux]         [k] 
> exit_to_user_mode_prepare
>     1.69%  sched-messaging  [kernel.vmlinux]         [k] try_to_wake_up
>     1.58%  sched-messaging  libc.so.6                [.] write
>     1.53%  sched-messaging  [kernel.vmlinux]         [k] psi_group_change
>     1.50%  sched-messaging  libc.so.6                [.] read
>     1.50%  sched-messaging  [kernel.vmlinux]         [k] pipe_read
>     1.39%  sched-messaging  [kernel.vmlinux]         [k] update_load_avg
>     1.39%  sched-messaging  [kernel.vmlinux]         [k] osq_lock
>     1.30%  sched-messaging  [kernel.vmlinux]         [k] update_curr
>     1.28%  swapper          [kernel.vmlinux]         [k] psi_group_change
>     1.16%  sched-messaging  [kernel.vmlinux]         [k] vfs_read
>     1.12%  sched-messaging  [kernel.vmlinux]         [k] vfs_write
>     1.10%  sched-messaging  [kernel.vmlinux]         [k] 
> entry_SYSRETQ_unsafe_stack
>     1.09%  sched-messaging  [kernel.vmlinux]         [k] __switch_to_asm
>     1.08%  sched-messaging  [kernel.vmlinux]         [k] do_syscall_64
>     1.06%  sched-messaging  [kernel.vmlinux]         [k] 
> select_task_rq_fair
>     1.03%  swapper          [kernel.vmlinux]         [k] update_cfs_group
>     1.00%  swapper          [kernel.vmlinux]         [k] rb_insert_color
> 
> # Base + reverted_new_mm_cid
> Threads:
> Total time: 7.847 [sec]
> 
>    12.14%  sched-messaging  [kernel.vmlinux]      [k] 
> native_queued_spin_lock_slowpath
>     8.86%  swapper          [kernel.vmlinux]      [k] 
> native_queued_spin_lock_slowpath
>     6.13%  sched-messaging  [kernel.vmlinux]      [k] copyin
>     5.54%  sched-messaging  [kernel.vmlinux]      [k] 
> apparmor_file_permission
>     3.59%  sched-messaging  [kernel.vmlinux]      [k] copyout
>     2.61%  sched-messaging  [kernel.vmlinux]      [k] osq_lock
>     2.48%  sched-messaging  [kernel.vmlinux]      [k] pipe_write
>     2.33%  sched-messaging  [kernel.vmlinux]      [k] 
> exit_to_user_mode_prepare
>     2.01%  sched-messaging  [kernel.vmlinux]      [k] 
> check_preemption_disabled
>     1.96%  sched-messaging  [kernel.vmlinux]      [k] __entry_text_start
>     1.91%  sched-messaging  libc.so.6             [.] write
>     1.77%  sched-messaging  libc.so.6             [.] read
>     1.64%  sched-messaging  [kernel.vmlinux]      [k] mutex_spin_on_owner
>     1.58%  sched-messaging  [kernel.vmlinux]      [k] pipe_read
>     1.52%  sched-messaging  [kernel.vmlinux]      [k] try_to_wake_up
>     1.38%  sched-messaging  [kernel.vmlinux]      [k] 
> ktime_get_coarse_real_ts64
>     1.35%  sched-messaging  [kernel.vmlinux]      [k] vfs_write
>     1.28%  sched-messaging  [kernel.vmlinux]      [k] 
> entry_SYSRETQ_unsafe_stack
>     1.28%  sched-messaging  [kernel.vmlinux]      [k] vfs_read
>     1.25%  sched-messaging  [kernel.vmlinux]      [k] do_syscall_64
>     1.22%  sched-messaging  [kernel.vmlinux]      [k] __fget_light
>     1.18%  sched-messaging  [kernel.vmlinux]      [k] mutex_lock
>     1.12%  sched-messaging  [kernel.vmlinux]      [k] file_update_time
>     1.04%  sched-messaging  [kernel.vmlinux]      [k] _copy_from_iter
>     1.01%  sched-messaging  [kernel.vmlinux]      [k] current_time
> 
> So with the reverted new_mm_cid patch, we are seeing a lot of time being 
> spent in
> native_queued_spin_lock_slowpath and yet, hackbench finishes faster.
> 
> I keep further digging into this please let me know if you have any 
> pointers for me.

Do you have CONFIG_SECURITY_APPARMOR=y ? Can you try without ?

I notice that apparmor_file_permission appears near the top of your
profiles, and apparmor uses an internal aa_buffers_lock spinlock,
which could possibly explain the top hits for
native_queued_spin_lock_slowpath. My current suspicion is that
the raw spinlock that was taken by "Base + reverted_new_mm_cid"
changed the contention pattern on the apparmor lock enough to
speed things up by pure accident.

Thanks,

Mathieu


> 
>>
>> This patch has recently been merged into the mm tree.
>>
>> Thanks,
>>
>> Mathieu
>>
> -- 
> Thanks and Regards,
> Swapnil

-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com