linux-kernel - Re: [PATCH v9 0/2] sched/fair: Scan cluster before scanning LLC in wake-up path

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Date:   Tue, 15 Aug 2023 19:16:17 +0800
From:   Yicong Yang <yangyicong@...wei.com>
To:     <peterz@...radead.org>
CC:     <yangyicong@...ilicon.com>, <rostedt@...dmis.org>,
        <bsegall@...gle.com>, <bristot@...hat.com>,
        <prime.zeng@...wei.com>, <jonathan.cameron@...wei.com>,
        <ego@...ux.vnet.ibm.com>, <srikar@...ux.vnet.ibm.com>,
        <linuxarm@...wei.com>, <21cnbao@...il.com>,
        <kprateek.nayak@....com>, <wuyun.abel@...edance.com>,
        <juri.lelli@...hat.com>, <vincent.guittot@...aro.org>,
        <dietmar.eggemann@....com>, <yu.c.chen@...el.com>,
        <tim.c.chen@...ux.intel.com>, <gautham.shenoy@....com>,
        <mgorman@...e.de>, <vschneid@...hat.com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <mingo@...hat.com>
Subject: Re: [PATCH v9 0/2] sched/fair: Scan cluster before scanning LLC in
 wake-up path

Hi Peter,

A gentle ping for this. Any further comment?

Thanks.

On 2023/7/19 17:28, Yicong Yang wrote:
> From: Yicong Yang <yangyicong@...ilicon.com>
> 
> This is the follow-up work to support cluster scheduler. Previously
> we have added cluster level in the scheduler for both ARM64[1] and
> X86[2] to support load balance between clusters to bring more memory
> bandwidth and decrease cache contention. This patchset, on the other
> hand, takes care of wake-up path by giving CPUs within the same cluster
> a try before scanning the whole LLC to benefit those tasks communicating
> with each other.
> 
> [1] 778c558f49a2 ("sched: Add cluster scheduler level in core and related Kconfig for ARM64")
> [2] 66558b730f25 ("sched: Add cluster scheduler level for x86")
> 
> Since we're using sd->groups->flags to determine a cluster, core should ensure
> the flags set correctly on domain generation. This is done by [*].
> 
> [*] https://lore.kernel.org/all/20230713013133.2314153-1-yu.c.chen@intel.com/
> 
> Change since v8:
> - Peter find cpus_share_lowest_cache() is weired so fallback to cpus_share_resources()
>   suggested in v4
> - Use sd->groups->flags to find the cluster when scanning, save one per-cpu pointer
> - Fix sched_cluster_active enabled incorrectly on domain degeneration
> - Use sched_cluster_active to avoid repeated check on non-cluster machines, per Gautham
> Link: https://lore.kernel.org/all/20230530070253.33306-1-yangyicong@huawei.com/
> 
> Change since v7:
> - Optimize by choosing prev_cpu/recent_used_cpu when possible after failed to
>   scanning for an idle CPU in cluster/LLC. Thanks Chen Yu for testing on Jacobsville
> Link: https://lore.kernel.org/all/20220915073423.25535-1-yangyicong@huawei.com/
> 
> Change for RESEND:
> - Collect tag from Chen Yu and rebase on the latest tip/sched/core. Thanks.
> Link: https://lore.kernel.org/lkml/20220822073610.27205-1-yangyicong@huawei.com/
> 
> Change since v6:
> - rebase on 6.0-rc1
> Link: https://lore.kernel.org/lkml/20220726074758.46686-1-yangyicong@huawei.com/
> 
> Change since v5:
> - Improve patch 2 according to Peter's suggestion:
>   - use sched_cluster_active to indicate whether cluster is active
>   - consider SMT case and use wrap iteration when scanning cluster
> - Add Vincent's tag
> Thanks.
> Link: https://lore.kernel.org/lkml/20220720081150.22167-1-yangyicong@hisilicon.com/
> 
> Change since v4:
> - rename cpus_share_resources to cpus_share_lowest_cache to be more informative, per Tim
> - return -1 when nr==0 in scan_cluster(), per Abel
> Thanks!
> Link: https://lore.kernel.org/lkml/20220609120622.47724-1-yangyicong@hisilicon.com/
> 
> Change since v3:
> - fix compile error when !CONFIG_SCHED_CLUSTER, reported by lkp test.
> Link: https://lore.kernel.org/lkml/20220608095758.60504-1-yangyicong@hisilicon.com/
> 
> Change since v2:
> - leverage SIS_PROP to suspend redundant scanning when LLC is overloaded
> - remove the ping-pong suppression
> - address the comment from Tim, thanks.
> Link: https://lore.kernel.org/lkml/20220126080947.4529-1-yangyicong@hisilicon.com/
> 
> Change since v1:
> - regain the performance data based on v5.17-rc1
> - rename cpus_share_cluster to cpus_share_resources per Vincent and Gautham, thanks!
> Link: https://lore.kernel.org/lkml/20211215041149.73171-1-yangyicong@hisilicon.com/
> 
> Barry Song (2):
>   sched: Add cpus_share_resources API
>   sched/fair: Scan cluster before scanning LLC in wake-up path
> 
>  include/linux/sched/sd_flags.h |  7 ++++
>  include/linux/sched/topology.h |  8 ++++-
>  kernel/sched/core.c            | 12 +++++++
>  kernel/sched/fair.c            | 59 +++++++++++++++++++++++++++++++---
>  kernel/sched/sched.h           |  2 ++
>  kernel/sched/topology.c        | 25 ++++++++++++++
>  6 files changed, 107 insertions(+), 6 deletions(-)
>