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From: Peter Oskolkov <posk@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: mingo@redhat.com, tglx@linutronix.de, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
	bristot@redhat.com, linux-kernel@vger.kernel.org,
	linux-mm@kvack.org, linux-api@vger.kernel.org, x86@kernel.org,
	pjt@google.com, avagin@google.com, jannh@google.com,
	tdelisle@uwaterloo.ca, posk@posk.io
Subject: Re: [RFC PATCH v2 4/5] sched: UMCG: add a blocked worker list
Date: Tue, 18 Jan 2022 09:16:59 -0800	[thread overview]
Message-ID: <CAPNVh5e+ijBCdvzZujWNUw7QnFt5Mdonw35ByuvcvzJu7gGjHQ@mail.gmail.com> (raw)
In-Reply-To: <YeU0nr6DfBCaH6UF@hirez.programming.kicks-ass.net>

On Mon, Jan 17, 2022 at 1:19 AM Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Thu, Jan 13, 2022 at 03:39:39PM -0800, Peter Oskolkov wrote:

[...]

> >
> > So this change basically decouples block/wake detection from
> > M:N threading in the sense that the number of servers is now
> > does not have to be M or N, but is more driven by the scalability
> > needs of the userspace application.
>
> So I don't object to having this blocking list, we had that early on in
> the discussions.
>
> *However*, combined with WF_CURRENT_CPU this 1:N userspace model doesn't
> really make sense, also combined with Proxy-Exec (if we ever get that
> sorted) it will fundamentally not work.
>
> More consideration is needed I think...

I was not very clear here. The intent of this change is not to make
1:N a good general approach, but to make "several running workers per
single server" a viable option.

My guess, based on some numbers/benchmarks from another project, is
that having a single server/runqueue per four or eight running
workers, properly aligned with (= affined to) an AMD chiplet, will be
the most performant solution, comparing to both a runqueue per single
running worker and to a global runqueue. On Intel this will probably
look like a single runqueue per core (2 running workers/HT threads).

So in this model a "server" represents a runqueue.

I'll reply to other active umcg discussions shortly.

  reply	other threads:[~2022-01-18 17:17 UTC|newest]

Thread overview: 11+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-13 23:39 [RFC PATCH v2 0/5] User Managed Concurrency Groups Peter Oskolkov
2022-01-13 23:39 ` [RFC PATCH v2 1/5] sched/umcg: add WF_CURRENT_CPU and externise ttwu Peter Oskolkov
2022-01-13 23:39 ` [RFC PATCH v2 2/5] x86/uaccess: Implement unsafe_try_cmpxchg_user() Peter Oskolkov
2022-01-13 23:39 ` [RFC PATCH v2 3/5] sched: User Mode Concurency Groups Peter Oskolkov
2022-01-13 23:39 ` [RFC PATCH v2 4/5] sched: UMCG: add a blocked worker list Peter Oskolkov
2022-01-17  9:19   ` Peter Zijlstra
2022-01-18 17:16     ` Peter Oskolkov [this message]
2022-01-27 15:37   ` Peter Zijlstra
2022-01-27 17:20     ` Peter Oskolkov
2022-01-13 23:39 ` [RFC PATCH v2 5/5] sched: UMCG: allow to sys_umcg_kick UMCG servers Peter Oskolkov
2022-01-27 16:35   ` Peter Zijlstra

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