linux-kernel - Re: [RFC][PATCH] spin loop arch primitives for busy waiting

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Message-ID: <20170407094349.f4hdqibbgl36s776@hirez.programming.kicks-ass.net>
Date:   Fri, 7 Apr 2017 11:43:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Will Deacon <will.deacon@....com>,
        Nicholas Piggin <npiggin@...il.com>,
        David Miller <davem@...emloft.net>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Anton Blanchard <anton@...ba.org>,
        linuxppc-dev list <linuxppc-dev@...abs.org>
Subject: Re: [RFC][PATCH] spin loop arch primitives for busy waiting

On Thu, Apr 06, 2017 at 10:31:46AM -0700, Linus Torvalds wrote:
> But maybe "monitor" is really cheap. I suspect it's microcoded,
> though, which implies "no".

On my IVB-EP (will also try on something newer):

MONITOR	~332 cycles
MWAIT	~224 cycles (C0, explicitly invalidated MONITOR)

So yes, expensive.