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Date: Fri, 20 Mar 2020 14:51:08 -0700 From: Andy Lutomirski <luto@...nel.org> To: Thomas Gleixner <tglx@...utronix.de> Cc: Andy Lutomirski <luto@...nel.org>, Kyung Min Park <kyung.min.park@...el.com>, X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>, Greg KH <gregkh@...uxfoundation.org>, Andi Kleen <ak@...ux.intel.com>, Tony Luck <tony.luck@...el.com>, "Raj, Ashok" <ashok.raj@...el.com>, "Ravi V. Shankar" <ravi.v.shankar@...el.com>, Fenghua Yu <fenghua.yu@...el.com> Subject: Re: [PATCH v2 2/2] x86/delay: Introduce TPAUSE delay On Fri, Mar 20, 2020 at 3:00 AM Thomas Gleixner <tglx@...utronix.de> wrote: > > Andy Lutomirski <luto@...nel.org> writes: > > On Thu, Mar 19, 2020 at 9:13 PM Kyung Min Park <kyung.min.park@...el.com> wrote: > >> void use_tsc_delay(void) > >> { > >> - if (delay_fn == delay_loop) > >> + if (static_cpu_has(X86_FEATURE_WAITPKG)) { > >> + delay_halt_fn = delay_halt_tpause; > >> + delay_fn = delay_halt; > >> + } else if (delay_fn == delay_loop) { > >> delay_fn = delay_tsc; > >> + } > >> } > > > > This is an odd way to dispatch: you're using static_cpu_has(), but > > you're using it once to populate a function pointer. Why not just put > > the static_cpu_has() directly into delay_halt() and open-code the > > three variants? > > Two: mwaitx and tpause. I was imagining there would also be a variant for systems with neither feature.
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