Messages in this thread | | | Date | Thu, 7 Jun 2018 09:34:27 +0800 | From | Feng Tang <> | Subject | Re: [RFC 2/2] x86, tsc: Enable clock for ealry printk timestamp |
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Hi Pavel,
Thanks for the revew.
On Wed, Jun 06, 2018 at 11:25:22AM -0400, Pavel Tatashin wrote: > Hi Feng, > > Using a global variable for this is not going to work, because you are adding a conditional branch and a load to a very hot path for the live of the system, not only for the duration of the boot.
Exactly. As I explained, I wanted to use the "__use_tsc" and "__sched_clock_stable" without creating new gloabl variables, but the problem is jump_label_init() can't be called that early, so I used "tsc_inited" temply just to show tsc_init() could be call early, and the printk timestamp could work much earlier.
Thanks, Feng
> > Pavel > > > > > +int tsc_inited; > > /* > > * TSC can be unstable due to cpufreq or due to unsynced TSCs > > */ > > @@ -192,7 +193,7 @@ static void set_cyc2ns_scale(unsigned long khz, int cpu, unsigned long long tsc_ > > */ > > u64 native_sched_clock(void) > > { > > - if (static_branch_likely(&__use_tsc)) { > > + if (static_branch_likely(&__use_tsc) || tsc_inited) { > > u64 tsc_now = rdtsc(); > > > > /* return the value in ns */ > > @@ -1387,30 +1391,16 @@ static int __init init_tsc_clocksource(void) > > */ > > device_initcall(init_tsc_clocksource); > > > > -void __init tsc_early_delay_calibrate(void) > > -{ > > - unsigned long lpj; > > - > > - if (!boot_cpu_has(X86_FEATURE_TSC)) > > - return; > > - > > - cpu_khz = x86_platform.calibrate_cpu(); > > - tsc_khz = x86_platform.calibrate_tsc(); > > - > > - tsc_khz = tsc_khz ? : cpu_khz; > > - if (!tsc_khz) > > - return; > > - > > - lpj = tsc_khz * 1000; > > - do_div(lpj, HZ); > > - loops_per_jiffy = lpj; > > -} > > - > > void __init tsc_init(void) > > { > > u64 lpj, cyc; > > int cpu; > > > > + if (tsc_inited) > > + return; > > + > > + tsc_inited = 1; > > + > > if (!boot_cpu_has(X86_FEATURE_TSC)) { > > setup_clear_cpu_cap(X86_FEATURE_TSC_DEADLINE_TIMER); > > return; > > @@ -1474,11 +1464,15 @@ void __init tsc_init(void) > > lpj = ((u64)tsc_khz * 1000); > > do_div(lpj, HZ); > > lpj_fine = lpj; > > + loops_per_jiffy = lpj; > > > > use_tsc_delay(); > > > > check_system_tsc_reliable(); > > > > + extern void early_set_sched_clock_stable(u64 sched_clock_offset); > > + early_set_sched_clock_stable(div64_u64(rdtsc() * 1000, tsc_khz)); > > + > > if (unsynchronized_tsc()) { > > mark_tsc_unstable("TSCs unsynchronized"); > > return; > > diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c > > index 10c83e7..6c5c22d 100644 > > --- a/kernel/sched/clock.c > > +++ b/kernel/sched/clock.c > > @@ -119,6 +119,13 @@ static void __scd_stamp(struct sched_clock_data *scd) > > scd->tick_raw = sched_clock(); > > } > > > > + > > +void early_set_sched_clock_stable(u64 sched_clock_offset) > > +{ > > + __sched_clock_offset = sched_clock_offset; > > + static_branch_enable(&__sched_clock_stable); > > +} > > + > > static void __set_sched_clock_stable(void) > > { > > struct sched_clock_data *scd; > > @@ -342,12 +349,14 @@ static u64 sched_clock_remote(struct sched_clock_data *scd) > > * > > * See cpu_clock(). > > */ > > + > > +extern int tsc_inited; > > u64 sched_clock_cpu(int cpu) > > { > > struct sched_clock_data *scd; > > u64 clock; > > > > - if (sched_clock_stable()) > > + if (sched_clock_stable() || tsc_inited) > > return sched_clock() + __sched_clock_offset; > > > > if (unlikely(!sched_clock_running)) > > > > > > > > > >>> > >>> If you have a dodgy part (sorry SKX), you'll just have to live with > >>> sched_clock starting late(r). > >>> > >>> Do not cobble things on the side, try and get the normal things running > >>> earlier.
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