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From: Thomas Gleixner <tglx@linutronix.de>
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To: Vishal Chourasia <vishalc@linux.ibm.com>, peterz@infradead.org,
 aboorvad@linux.ibm.com
Cc: boqun.feng@gmail.com, frederic@kernel.org, joelagnelf@nvidia.com,
 josh@joshtriplett.org, linux-kernel@vger.kernel.org,
 neeraj.upadhyay@kernel.org, paulmck@kernel.org, rcu@vger.kernel.org,
 rostedt@goodmis.org, srikar@linux.ibm.com, sshegde@linux.ibm.com,
 urezki@gmail.com, samir@linux.ibm.com, vishalc@linux.ibm.com
Subject: Re: [PATCH v3 2/2] cpuhp: Expedite RCU grace periods during SMT
 operations
In-Reply-To: <20260218083915.660252-6-vishalc@linux.ibm.com>
References: <20260218083915.660252-2-vishalc@linux.ibm.com>
 <20260218083915.660252-6-vishalc@linux.ibm.com>
Date: Wed, 25 Mar 2026 20:10:30 +0100
Message-ID: <87fr5nendl.ffs@tglx>
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On Wed, Feb 18 2026 at 14:09, Vishal Chourasia wrote:
> Expedite synchronize_rcu during the SMT mode switch operation when
> initiated via /sys/devices/system/cpu/smt/control interface
>
> SMT mode switch operation i.e. between SMT 8 to SMT 1 or vice versa and
> others are user driven operations and therefore should complete as soon
> as possible. Switching SMT states involves iterating over a list of CPUs
> and performing hotplug operations. It was found these transitions took
> significantly large amount of time to complete particularly on
> high-core-count systems.

This changelog is neither explaining the underlying problem, nor
explaining why expedite solves it and does not contain numbers which
justify the change.

Thanks,

        tglx