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From: Thomas Gleixner <tglx@linutronix.de>
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Mathias Stearn <mathias@mongodb.com>, Dmitry Vyukov
 <dvyukov@google.com>, Jinjie Ruan <ruanjinjie@huawei.com>,
 linux-man@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>, Mathieu
 Desnoyers <mathieu.desnoyers@efficios.com>, Catalin Marinas
 <catalin.marinas@arm.com>, Will Deacon <will@kernel.org>, Boqun Feng
 <boqun.feng@gmail.com>, "Paul E. McKenney" <paulmck@kernel.org>, Chris
 Kennelly <ckennelly@google.com>, regressions@lists.linux.dev,
 linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Ingo
 Molnar <mingo@kernel.org>, Blake Oler <blake.oler@mongodb.com>
Subject: Re: [REGRESSION] rseq: refactoring in v6.19 broke everyone on arm64
 and tcmalloc everywhere
In-Reply-To: <20260424150318.GE641209@noisy.programming.kicks-ass.net>
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Date: Fri, 24 Apr 2026 21:44:16 +0200
Message-ID: <87se8kywhb.ffs@tglx>
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On Fri, Apr 24 2026 at 17:03, Peter Zijlstra wrote:
> On Fri, Apr 24, 2026 at 04:16:08PM +0200, Thomas Gleixner wrote:
>> > I was really hoping that we would only need to do the "redundant"
>> > cpu_id_start writes would only be needed on membarrier_rseq IPIs where
>> > it really is a pay-for-what-you-use functionality,
>> 
>> That's fine and can be solved without adding this sequence overhead into
>> the scheduler hotpath.
>
> Something like so? (probably needs help for !GENERIC bits)

Yes and yes :)

Let me stare at that !generic tif bits case.