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Date: Wed, 21 Jun 2023 14:51:42 -0400
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Swapnil Sapkal <Swapnil.Sapkal@....com>,
Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
Aaron Lu <aaron.lu@...el.com>, x86@...nel.org,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [tip: sched/core] sched: Fix performance regression introduced by
mm_cid
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
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