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Date: Tue, 18 Jul 2023 11:31:58 +0530
From: Swapnil Sapkal <Swapnil.Sapkal@....com>
To: Mathieu Desnoyers <mathieu.desnoyers@...icios.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
Hello Mathieu ,
On 7/14/2023 8:25 PM, Mathieu Desnoyers wrote:
> On 7/14/23 02:02, Swapnil Sapkal wrote:
>> Hello Mathieu,
>>
>> On 6/22/2023 12:21 AM, Mathieu Desnoyers wrote:
>>> 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 ?
>>>
>> Sorry for the delay in response. My system was busy running some workloads. I tried
>> running hackbench disabling apparmor, looks like apparmor is not the culprit here.
>> Below are the results with apparmor disabled:
>>
>> Test: Base Base + Reverted_new_mmcid Base+Apparmour_disabled
>> 1-groups: 2.81 (0.00 pct) 2.79 (0.71 pct) 2.79 (0.71 pct)
>> 2-groups: 3.25 (0.00 pct) 3.25 (0.00 pct) 3.20 (1.53 pct)
>> 4-groups: 3.44 (0.00 pct) 3.28 (4.65 pct) 3.43 (0.29 pct)
>> 8-groups: 3.52 (0.00 pct) 3.42 (2.84 pct) 3.53 (-0.28 pct)
>> 16-groups: 5.65 (0.00 pct) 4.52 (20.00 pct) 5.67 (-0.35 pct)
>
> Can you provide the kernel config file associated with this
> test ? I would also need to see ibs profiles showing the
> functions using most cpu, especially spinlocks and their
> callers.
>
I have attached kernel config with this mail.
> My working hypothesis is that adding the rseq-mm-cid spinlock
> in the scheduler improves performances of your benchmark because
> it lessens the contention on _another_ lock somewhere else.
>
> Note that we've just received a brand new 2 sockets,
> 96 cores/socket AMD machine at EfficiOS. We've bought it to
> increase our coverage of scalability testing. With this I should
> be able to reproduce those regressions on my end, which should
> facilitate the investigation.
>
> Thanks!
>
> Mathieu
>
>
>>
>> Thanks,
>> Swapnil
>>
>>> 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
>>>
>
--
Thanks and regards,
Swapnil
View attachment "mmcid.config" of type "text/plain" (277598 bytes)
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