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 18:08:05 +0900 [thread overview]
Message-ID: <ZYVR9U47MkpecqQu@mac> (raw)
In-Reply-To: <CAJhGHyDyWBCSH_41cU7TokbDTE=vknLjLKYMQUtN8LyUsvg9dw@mail.gmail.com>
Hello,
On Fri, Dec 22, 2023 at 04:04:27PM +0800, Lai Jiangshan wrote:
> The current "max_active enforcement domain" is just a historical accident.
I mean, the part that it's bound to NUMA is accidental but the fact that we
need an enforcement domain which is closer to the whole machine isn't. Most
users don't depend on max_active limit but there are a number of users that
do and what they usually want to express is "I want to be able to saturate
the whole machine but avoid creating pointless over-saturation", which
usually comes down to some multiples of the number of CPUs.
Note that there may be a single issuer or multiple issuers and we want to be
able to saturate the machine while avoding over-saturation in both cases. If
we segment max_limit enforcement to smaller units like CPUs or L3 caches,
there's no good way to express these constraints. A number which is too
smaller for single issuer case is already too big for multiple issuer case.
I tried to explain the conundrum in the cover letter but if that's not
sufficient, we can keep discussing. It'd be also useful to read what Naohiro
reported as that shows the problem pretty well.
> IMO, it is better to change the semantics of max_active and the related
> alloc_workqueue() callers rather than add a large bulk of complicated
> code. Most of alloc_workqueue() are called with max_active=0, so it is
> feasible.
Yeah, I mean, if we can, that'd be simpler. I don't think we can. It's a
rather fundamental problem. If you have concrete suggestions, please feel
free to share.
Thanks.
--
tejun
next prev parent reply other threads:[~2023-12-22 9:08 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-20 7:24 [PATCHSET wq/for-6.8] workqueue: Implement system-wide max_active for unbound workqueues 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
2023-12-22 8:04 ` Lai Jiangshan
2023-12-22 9:08 ` Tejun Heo [this message]
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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