Messages in this thread | | | From | "Park, Kyung Min" <> | Subject | RE: [PATCH v2 2/2] x86/delay: Introduce TPAUSE delay | Date | Mon, 30 Mar 2020 23:42:37 +0000 |
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Hi Andy/Thomas,
On Fri, Mar 20, 2020 at 4:23 PM Thomas Gleixner <tglx@linutronix.de> wrote: > > > > Andy Lutomirski <luto@kernel.org> writes: > > > > > On Fri, Mar 20, 2020 at 3:00 AM Thomas Gleixner <tglx@linutronix.de> > wrote: > > >> > > >> Andy Lutomirski <luto@kernel.org> writes: > > >> > On Thu, Mar 19, 2020 at 9:13 PM Kyung Min Park > <kyung.min.park@intel.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. > > > > Oh I see, you want to get rid of both function pointers. That's tricky. > > > > The boot time function is delay_loop() which is using the magic (1 << > > 12) boot time value until calibration in one way or the other happens > > and something calls use_tsc_delay() or use_mwaitx_delay(). Yes, that's > > all horrible but X86_FEATURE_TSC is unusable for this. > > > > Let me think about it. > > This is definitely not worth overoptimizing. It's a *delay* function > -- the retpoline isn't going to kill us :)
Since the use_tsc_delay() is used just once in __init tsc_init(), how about adding "__init" to the use_tsc_delay() and keep these function pointers?
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