From: Tejun Heo <tj@kernel.org>
To: Lai Jiangshan <jiangshanlai@gmail.com>
Cc: linux-kernel@vger.kernel.org, Naohiro.Aota@wdc.com, kernel-team@meta.com
Subject: Re: [PATCHSET wq/for-6.8] workqueue: Implement system-wide max_active for unbound workqueues
Date: Fri, 22 Dec 2023 08:01:35 +0900 [thread overview]
Message-ID: <ZYTDz10ohj0kokum@mtj.duckdns.org> (raw)
In-Reply-To: <CAJhGHyACBBW5wnYTTz7S+AgLMhLYOsfxTnN6VHodCgECqEFeEg@mail.gmail.com>
Hello, Lai.
On Wed, Dec 20, 2023 at 05:20:18PM +0800, Lai Jiangshan wrote:
> The patchset seems complicated to me. For me, reverting a bit to the behavior
> of 636b927eba5b ("workqueue: Make unbound workqueues to use per-cpu
> pool_workqueues"), like the following code (untested, just for showing
> the idea),
> seems simpler.
>
> max_active will have the same behavior as before if the wq is configured
> with WQ_AFFN_NUMA. For WQ_AFFN_{CPU|SMT|CACHE}, the problem
> isn't fixed.
Yeah, it is complicated but the complications come from the fact that the
domain we count nr_active can't match the worker_pools, and that's because
unbound workqueue behavior is noticeably worse if we let them roam across L3
boundaries on modern processors with multiple chiplets or otherwise
segmented L3 caches.
We need WQ_AFFN_CACHE to behave well on these chips and max_active
enforcement breaks if we keep them tied to pool in such cases, so I'm afraid
our hands are tied here. The hardware has changed and we have to adapt to
it. In this case, that comes at the cost of extra complexity to divorce
max_active enforcement domain from worker_pool boundaries.
Thanks.
--
tejun
next prev parent reply other threads:[~2023-12-21 23:01 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-20 7:24 Tejun Heo
2023-12-20 7:24 ` [PATCH 01/10] workqueue: Move pwq->max_active to wq->max_active Tejun Heo
2023-12-26 9:13 ` Lai Jiangshan
2023-12-26 20:05 ` Tejun Heo
2023-12-26 21:36 ` Tejun Heo
2023-12-20 7:24 ` [PATCH 02/10] workqueue: Factor out pwq_is_empty() Tejun Heo
2023-12-20 7:24 ` [PATCH 03/10] workqueue: Replace pwq_activate_inactive_work() with [__]pwq_activate_work() Tejun Heo
2023-12-20 7:24 ` [PATCH 04/10] workqueue: Move nr_active handling into helpers Tejun Heo
2023-12-26 9:12 ` Lai Jiangshan
2023-12-26 20:06 ` Tejun Heo
2023-12-20 7:24 ` [PATCH 05/10] workqueue: Make wq_adjust_max_active() round-robin pwqs while activating Tejun Heo
2023-12-20 7:24 ` [PATCH 06/10] workqueue: Add first_possible_node and node_nr_cpus[] Tejun Heo
2023-12-20 7:24 ` [PATCH 07/10] workqueue: Move pwq_dec_nr_in_flight() to the end of work item handling Tejun Heo
2023-12-20 7:24 ` [PATCH 08/10] workqueue: Introduce struct wq_node_nr_active Tejun Heo
2023-12-26 9:14 ` Lai Jiangshan
2023-12-26 20:12 ` Tejun Heo
2023-12-20 7:24 ` [PATCH 09/10] workqueue: Implement system-wide nr_active enforcement for unbound workqueues Tejun Heo
2023-12-20 7:24 ` [PATCH 10/10] workqueue: Reimplement ordered workqueue using shared nr_active Tejun Heo
2024-01-13 0:18 ` Tejun Heo
2023-12-20 9:20 ` [PATCHSET wq/for-6.8] workqueue: Implement system-wide max_active for unbound workqueues Lai Jiangshan
2023-12-21 23:01 ` Tejun Heo [this message]
2023-12-22 8:04 ` Lai Jiangshan
2023-12-22 9:08 ` Tejun Heo
2024-01-05 2:44 ` Naohiro Aota
2024-01-12 0:49 ` Tejun Heo
2024-01-13 0:17 ` Tejun Heo
2024-01-15 5:46 ` Naohiro Aota
2024-01-16 21:04 ` Tejun Heo
2024-01-30 2:24 ` Naohiro Aota
2024-01-30 16:11 ` Tejun Heo
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