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Message-ID: <c044d6001cf4ad25a8d13ba64c1d891721c16abd.camel@intel.com>
Subject: Re: [PATCH v3 3/3] x86/delay: Introduce TPAUSE delay
From:   km <kyung.min.park@intel.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        "Luck, Tony" <tony.luck@intel.com>
Cc:     "x86@kernel.org" <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
        "hpa@zytor.com" <hpa@zytor.com>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        "Raj, Ashok" <ashok.raj@intel.com>,
        "Shankar, Ravi V" <ravi.v.shankar@intel.com>,
        "Yu, Fenghua" <fenghua.yu@intel.com>
Date:   Wed, 15 Apr 2020 12:57:16 -0700
In-Reply-To: <20200414180545.GE2483@worktop.programming.kicks-ass.net>
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         <3908561D78D1C84285E8C5FCA982C28F7F5E3E80@ORSMSX115.amr.corp.intel.com>
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Precedence: bulk

Hi Peter,

On Tue, 2020-04-14 at 20:05 +0200, Peter Zijlstra wrote:
> On Tue, Apr 14, 2020 at 06:00:21PM +0000, Luck, Tony wrote:
> > > > +static inline void __tpause(u32 ecx, u32 edx, u32 eax)
> > > > +{
> > > > +	/* "tpause %ecx, %edx, %eax;" */
> > > > +	asm volatile(".byte 0x66, 0x0f, 0xae, 0xf1\t\n"
> > > > +		     :
> > > > +		     : "c"(ecx), "d"(edx), "a"(eax));
> > > > +}
> > > 
> > > Can we please get a comment stating from what binutils version
> > > this
> > > opcode has a mnemonic? That way, when we raise the minimum
> > > binutils
> > > version we can easily grep and find such things.
> > 
> > Or maybe use arch/x86/Kconfig.assembler to set up a
> > CONFIG_AS_TPAUSE?
> > 
> > Then the code can read something like (syntax may need fixing)
> > 
> > #ifdef CONFIG_AS_TPAUSE
> > 		asm volatile("tpause %ecx\n", : : "c"(ecx), "d"(edx),
> > "a"(eax));
> > #else
> > 		asm volatile(".byte hex gibberish ...
> > #endif
> 
> Then we still need a comment to know when we can kill that...

Thanks. I'll update in next patch.