Messages in this thread | | | Date | Wed, 13 Jun 2018 15:29:46 +0800 | From | Feng Tang <> | Subject | Re: [RFC 2/2] x86, tsc: Enable clock for ealry printk timestamp |
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On Wed, Jun 06, 2018 at 05:38:33PM +0800, Feng Tang wrote: > On Sat, Jun 02, 2018 at 12:12:13AM +0800, Feng Tang wrote: > > Hi Peter and all, > > > > Hi Peter and Petr, > > > > Thanks for your suggestions, will try to find a cleaner and less hacky way, > > and it may take some time as dealing with all kinds of TSC is tricky :) > > > > - Feng > > > > On Thu, May 31, 2018 at 05:52:10PM +0200, Peter Zijlstra wrote: > > > On Thu, May 31, 2018 at 03:55:42PM +0200, Petr Mladek wrote: > > > > I wonder if we could get some cleaner integration into the timer and > > > > printk code. > > > > > > Yes, these patches are particularly horrific.. > > > > > > There were some earlier patches by Pavel Tatashin, which attempted do > > > get things running earlier. > > > > > > http://lkml.kernel.org/r/20180209211143.16215-1-pasha.tatashin@oracle.com > > > > > > I'm not entirely happy with that, but I never did get around to > > > reviewing that last version :-( In particuarly, now that you made me > > > look, I dislike his patch 6 almost as much as these patches. > > > > > > The idea was to get regular sched_clock() running earlier, not to botch > > > some early_sched_clock() into it. > > > > > > Basically run calibrate_tsc() earlier (like _waaay_ earlier, it doesn't > > > rely on anything other than CPUID) and if you have a recent part (with > > > exception of SKX) you'll get a usable tsc rate (and TSC_RELIABLE) and > > > things will work. > > > I just did a hacky experiment by moving the tsc_init()earlier into > setup_arch() and remove the tsc_early_delay_calibrate(). The printk stamp > does start working much earlier! > > > But the __use_tsc and __sched_clock_stable are relying on jump_label, > which can't be used so early (I tried to call the jump_label_init() before > tsc_init(), but kernel crashs, and I worked around it for now).
Just figured out the kernel crash when taking jump_label_init() earlier into setup_arch(), the tsc_init() will enable static_key __use_tsc
static_key_enable __jump_label_update arch_jump_label_transform __jump_label_transform text_poke_bp text_poke
text_poke() will involve page , but paging is not initialized so early yet, so it triggers a panic.
Beside this __use_tsc, the sched_clock also has one static key __sched_clock_stable
Thanks, Feng
> > Please review the debug patch, thanks! > > --- > diff --git a/arch/x86/kernel/setup.c b/arch/x86/kernel/setup.c > index 5c623df..b636888 100644 > --- a/arch/x86/kernel/setup.c > +++ b/arch/x86/kernel/setup.c > @@ -1201,7 +1201,8 @@ void __init setup_arch(char **cmdline_p) > kvmclock_init(); > #endif > > - tsc_early_delay_calibrate(); > + tsc_init(); > + > if (!early_xdbc_setup_hardware()) > early_xdbc_register_console(); > > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c > index 4008dd6..8288f39 100644 > --- a/arch/x86/kernel/tsc.c > +++ b/arch/x86/kernel/tsc.c > @@ -33,6 +33,7 @@ EXPORT_SYMBOL(cpu_khz); > unsigned int __read_mostly tsc_khz; > EXPORT_SYMBOL(tsc_khz); > > +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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