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From: Peter Zijlstra <peterz@infradead.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	"Paul E . McKenney" <paulmck@kernel.org>,
	Boqun Feng <boqun.feng@gmail.com>,
	"H . Peter Anvin" <hpa@zytor.com>, Paul Turner <pjt@google.com>,
	linux-api@vger.kernel.org, Christian Brauner <brauner@kernel.org>,
	Florian Weimer <fw@deneb.enyo.de>,
	David.Laight@aculab.com, carlos@redhat.com,
	Peter Oskolkov <posk@posk.io>,
	Alexander Mikhalitsyn <alexander@mihalicyn.com>,
	Chris Kennelly <ckennelly@google.com>
Subject: Re: [PATCH v5 08/24] sched: Introduce per memory space current virtual cpu id
Date: Tue, 8 Nov 2022 14:04:46 +0100	[thread overview]
Message-ID: <Y2pT7ij/TcI4EmH6@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20221103200359.328736-9-mathieu.desnoyers@efficios.com>

On Thu, Nov 03, 2022 at 04:03:43PM -0400, Mathieu Desnoyers wrote:

> The credit goes to Paul Turner (Google) for the vcpu_id idea. This
> feature is implemented based on the discussions with Paul Turner and
> Peter Oskolkov (Google), but I took the liberty to implement scheduler
> fast-path optimizations and my own NUMA-awareness scheme. The rumor has
> it that Google have been running a rseq vcpu_id extension internally at
> Google in production for a year. The tcmalloc source code indeed has
> comments hinting at a vcpu_id prototype extension to the rseq system
> call [1].

Re NUMA thing -- that means that on a 512 node system a single threaded
task can still observe 512 separate vcpu-ids, right?

Also, said space won't be dense.

The main selling point of the whole vcpu-id scheme was that the id space
is dense and not larger than min(nr_cpus, nr_threads), which then gives
useful properties.

But I'm not at all seeing how the NUMA thing preserves that.

Also; given the utter mind-bendiness of the NUMA thing; should it go
into it's own patch; introduce the regular plain old vcpu first, and
then add things to it -- that also allows pushing those weird cpumask
ops you've created later into the series.

  parent reply	other threads:[~2022-11-08 13:05 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-03 20:03 [PATCH v5 00/24] RSEQ node id and virtual cpu id extensions Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 01/24] rseq: Introduce feature size and alignment ELF auxiliary vector entries Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 02/24] rseq: Introduce extensible rseq ABI Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 03/24] rseq: Extend struct rseq with numa node id Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 04/24] selftests/rseq: Use ELF auxiliary vector for extensible rseq Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 05/24] selftests/rseq: Implement rseq numa node id field selftest Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 06/24] lib: Implement find_{first,next,nth}_notandnot_bit, find_first_andnot_bit Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 07/24] cpumask: Implement cpumask_{first,next}_{not,}andnot Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 08/24] sched: Introduce per memory space current virtual cpu id Mathieu Desnoyers
2022-11-08 13:00   ` Peter Zijlstra
2022-11-08 19:45     ` Mathieu Desnoyers
2022-11-08 13:04   ` Peter Zijlstra [this message]
2022-11-08 20:07     ` Mathieu Desnoyers
2022-11-09 10:19       ` Peter Zijlstra
2022-11-09  9:28   ` Peter Zijlstra
2022-11-09 15:04     ` Mathieu Desnoyers
2022-11-09  9:42   ` Peter Zijlstra
2022-11-09 15:09     ` Mathieu Desnoyers
2022-11-11  4:41   ` Andy Lutomirski
2022-11-11 14:18     ` Mathieu Desnoyers
2022-11-14 20:49       ` Sean Christopherson
2022-11-17 17:19         ` Mathieu Desnoyers
2022-11-17 19:10           ` Sean Christopherson
2022-11-17 19:42             ` Mathieu Desnoyers
2022-11-17 21:15               ` Sean Christopherson
2022-11-21 19:00                 ` Mathieu Desnoyers
2022-11-21 19:52                   ` Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 09/24] rseq: Extend struct rseq with per memory space vcpu id Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 10/24] selftests/rseq: Remove RSEQ_SKIP_FASTPATH code Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 11/24] selftests/rseq: Implement rseq vm_vcpu_id field support Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 12/24] selftests/rseq: x86: Template memory ordering and percpu access mode Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 13/24] selftests/rseq: arm: " Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 14/24] selftests/rseq: arm64: " Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 15/24] selftests/rseq: mips: " Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 16/24] selftests/rseq: ppc: " Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 17/24] selftests/rseq: s390: " Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 18/24] selftests/rseq: riscv: " Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 19/24] selftests/rseq: Implement basic percpu ops vm_vcpu_id test Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 20/24] selftests/rseq: Implement parametrized " Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 21/24] selftests/rseq: x86: Implement rseq_load_u32_u32 Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 22/24] selftests/rseq: Implement numa node id vs vm_vcpu_id invariant test Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 23/24] selftests/rseq: parametrized test: Report/abort on negative cpu id Mathieu Desnoyers
2022-11-03 20:03 ` [PATCH v5 24/24] tracing/rseq: Add mm_vcpu_id field to rseq_update Mathieu Desnoyers

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