linux-kernel - Re: [PATCH 0/3] IPI: Avoid to use 2 cache lines for one call_single

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Date:   Wed, 2 Aug 2017 08:54:40 -0500 (CDT)
From:   Christopher Lameter <cl@...ux.com>
To:     "Huang, Ying" <ying.huang@...el.com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org, Tejun Heo <tj@...nel.org>,
        Joerg Roedel <joro@...tes.org>, Ingo Molnar <mingo@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Borislav Petkov <bp@...e.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Juergen Gross <jgross@...e.com>, Aaron Lu <aaron.lu@...el.com>
Subject: Re: [PATCH 0/3] IPI: Avoid to use 2 cache lines for one
 call_single_data

On Wed, 2 Aug 2017, Huang, Ying wrote:

> To allocate cache line size aligned percpu memory dynamically,
> alloc_percpu_aligned() is introduced and used in iova drivers too.

alloc_percpu() already aligns objects as specified when they are declared.

Moreover the function is improperly named since it aligns
to a cacheline(). If you want this then you would use

alloc_percpu_cacheline_aligned()

But then the alignment can already be requested by adding
__cacheline_aligned to the per cpu definition.