linux-kernel - Re: [PATCH 2/2] x86/asm/delay: Introduce TPAUSE delay

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Date:   Wed, 26 Feb 2020 13:20:34 -0800
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Kyung Min Park <kyung.min.park@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...hat.com,
        hpa@...or.com, gregkh@...uxfoundation.org, ashok.raj@...el.com,
        ravi.v.shankar@...el.com, fenghua.yu@...el.com
Subject: Re: [PATCH 2/2] x86/asm/delay: Introduce TPAUSE delay

On Wed, Feb 26, 2020 at 01:10:40PM -0800, Andi Kleen wrote:
> On Wed, Feb 26, 2020 at 11:10:58AM -0800, Kyung Min Park wrote:
> > TPAUSE instructs the processor to enter an implementation-dependent
> > optimized state. The instruction execution wakes up when the time-stamp
> > counter reaches or exceeds the implicit EDX:EAX 64-bit input value.
> > The instruction execution also wakes up due to the expiration of
> > the operating system time-limit or by an external interrupt
> 
> This is actually a behavior change. Today's udelay() will continue
> after processing the interrupt. Your patches don't

The instruction level TPAUSE is called inside delay_wait()
that checks to see of we were interrupted early and loops to issue
another TPAUSE if needed.

-Tony