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Date:   Wed, 3 Apr 2019 19:16:35 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Waiman Long <longman@redhat.com>
Cc:     Alex Kogan <alex.kogan@oracle.com>, linux@armlinux.org.uk,
        mingo@redhat.com, will.deacon@arm.com, arnd@arndb.de,
        linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de,
        hpa@zytor.com, x86@kernel.org, steven.sistare@oracle.com,
        daniel.m.jordan@oracle.com, dave.dice@oracle.com,
        rahul.x.yadav@oracle.com
Subject: Re: [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow
 path of qspinlock
Message-ID: <20190403171635.GM4038@hirez.programming.kicks-ass.net>
References: <20190329152006.110370-1-alex.kogan@oracle.com>
 <20190329152006.110370-4-alex.kogan@oracle.com>
 <60a3a2d8-d222-73aa-2df1-64c9d3fa3241@redhat.com>
 <20190402094320.GM11158@hirez.programming.kicks-ass.net>
 <9ec3d8dc-d1e0-1b8a-5e00-ba92b9756c58@redhat.com>
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On Wed, Apr 03, 2019 at 12:33:20PM -0400, Waiman Long wrote:
> static inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32
> val)
> {
> ??????? if (static_branch_unlikely(&use_numa_spinlock))
> ??????????????? numa_queued_spin_lock_slowpath(lock, val);
> ??????? else???
> ??????????????? native_queued_spin_lock_slowpath(lock, val);
> }

That's horrible for the exact reason you state.

> Alternatively, we can also call numa_queued_spin_lock_slowpath() in
> native_queued_spin_lock_slowpath() if we don't want to increase the code
> size of spinlock call sites.

Yeah, still don't much like that though, we're littering the fast path
of that slow path with all sorts of crap.