> > I changed cpu_serializing_counter() with tsc_get_timecount() as they > > were the same function now that msr is gone. Hope that is not too gross. > > That doesn't work as tsc_get_timecount() returns a 32-bit integer. > > <pirofti> I can not just rdtsc because that means changing the drift max > > I don't understand that comment. Whether you add the previous skew or > not makes no difference when calculating the new skew since you're > adding the same value to both TSC counts when calculating the > difference. The measured skew shouldn't change. And when calculating > the drift you simply subtract the new skew from the old skew. So > nothing changes. Or am I missing something? >
Nope. Double checked with my fears about the drift and, as stated on the channel, it was a false alarm. :) Index: arch/amd64/amd64/cpu.c =================================================================== RCS file: /cvs/src/sys/arch/amd64/amd64/cpu.c,v retrieving revision 1.137 diff -u -p -u -p -r1.137 cpu.c --- arch/amd64/amd64/cpu.c 28 May 2019 18:17:01 -0000 1.137 +++ arch/amd64/amd64/cpu.c 9 Aug 2019 11:33:41 -0000 @@ -754,6 +754,10 @@ cpu_init(struct cpu_info *ci) cr4 = rcr4(); lcr4(cr4 & ~CR4_PGE); lcr4(cr4); + + /* Synchronize TSC */ + if (cold && !CPU_IS_PRIMARY(ci)) + tsc_sync_ap(ci); #endif } @@ -808,6 +812,7 @@ void cpu_start_secondary(struct cpu_info *ci) { int i; + u_long s; ci->ci_flags |= CPUF_AP; @@ -828,6 +833,18 @@ cpu_start_secondary(struct cpu_info *ci) printf("dropping into debugger; continue from here to resume boot\n"); db_enter(); #endif + } else { + /* + * Synchronize time stamp counters. Invalidate cache and + * synchronize twice (in tsc_sync_bp) to minimize possible + * cache effects. Disable interrupts to try and rule out any + * external interference. + */ + s = intr_disable(); + wbinvd(); + tsc_sync_bp(ci); + intr_restore(s); + printf("TSC skew=%lld\n", (long long)ci->ci_tsc_skew); } if ((ci->ci_flags & CPUF_IDENTIFIED) == 0) { @@ -852,6 +869,8 @@ void cpu_boot_secondary(struct cpu_info *ci) { int i; + int64_t drift; + u_long s; atomic_setbits_int(&ci->ci_flags, CPUF_GO); @@ -864,6 +883,17 @@ cpu_boot_secondary(struct cpu_info *ci) printf("dropping into debugger; continue from here to resume boot\n"); db_enter(); #endif + } else if (cold) { + /* Synchronize TSC again, check for drift. */ + drift = ci->ci_tsc_skew; + s = intr_disable(); + wbinvd(); + tsc_sync_bp(ci); + intr_restore(s); + drift -= ci->ci_tsc_skew; + printf("TSC skew=%lld drift=%lld\n", + (long long)ci->ci_tsc_skew, (long long)drift); + tsc_sync_drift(drift); } } @@ -888,7 +918,14 @@ cpu_hatch(void *v) panic("%s: already running!?", ci->ci_dev->dv_xname); #endif + /* + * Synchronize the TSC for the first time. Note that interrupts are + * off at this point. + */ + wbinvd(); ci->ci_flags |= CPUF_PRESENT; + ci->ci_tsc_skew = 0; /* reset on resume */ + tsc_sync_ap(ci); lapic_enable(); lapic_startclock(); Index: arch/amd64/amd64/tsc.c =================================================================== RCS file: /cvs/src/sys/arch/amd64/amd64/tsc.c,v retrieving revision 1.11 diff -u -p -u -p -r1.11 tsc.c --- arch/amd64/amd64/tsc.c 6 Jun 2019 19:43:35 -0000 1.11 +++ arch/amd64/amd64/tsc.c 9 Aug 2019 11:33:41 -0000 @@ -1,8 +1,10 @@ /* $OpenBSD: tsc.c,v 1.11 2019/06/06 19:43:35 kettenis Exp $ */ /* + * Copyright (c) 2008 The NetBSD Foundation, Inc. * Copyright (c) 2016,2017 Reyk Floeter <r...@openbsd.org> * Copyright (c) 2017 Adam Steen <a...@adamsteen.com.au> * Copyright (c) 2017 Mike Belopuhov <m...@openbsd.org> + * Copyright (c) 2019 Paul Irofti <piro...@openbsd.org> * * Permission to use, copy, modify, and distribute this software for any * purpose with or without fee is hereby granted, provided that the above @@ -20,6 +22,7 @@ #include <sys/param.h> #include <sys/systm.h> #include <sys/timetc.h> +#include <sys/atomic.h> #include <machine/cpu.h> #include <machine/cpufunc.h> @@ -33,6 +36,12 @@ int tsc_recalibrate; uint64_t tsc_frequency; int tsc_is_invariant; +#define TSC_DRIFT_MAX 250 +int64_t tsc_drift_observed; + +volatile int64_t tsc_sync_val; +volatile struct cpu_info *tsc_sync_cpu; + uint tsc_get_timecount(struct timecounter *tc); struct timecounter tsc_timecounter = { @@ -172,10 +181,8 @@ calibrate_tsc_freq(void) return; tsc_frequency = freq; tsc_timecounter.tc_frequency = freq; -#ifndef MULTIPROCESSOR if (tsc_is_invariant) tsc_timecounter.tc_quality = 2000; -#endif } void @@ -194,14 +201,13 @@ cpu_recalibrate_tsc(struct timecounter * uint tsc_get_timecount(struct timecounter *tc) { - return rdtsc(); + return rdtsc() + curcpu()->ci_tsc_skew; } void tsc_timecounter_init(struct cpu_info *ci, uint64_t cpufreq) { - if (!(ci->ci_flags & CPUF_PRIMARY) || - !(ci->ci_flags & CPUF_CONST_TSC) || + if (!(ci->ci_flags & CPUF_CONST_TSC) || !(ci->ci_flags & CPUF_INVAR_TSC)) return; @@ -211,9 +217,7 @@ tsc_timecounter_init(struct cpu_info *ci /* Newer CPUs don't require recalibration */ if (tsc_frequency > 0) { tsc_timecounter.tc_frequency = tsc_frequency; -#ifndef MULTIPROCESSOR tsc_timecounter.tc_quality = 2000; -#endif } else { tsc_recalibrate = 1; tsc_frequency = cpufreq; @@ -221,5 +225,103 @@ tsc_timecounter_init(struct cpu_info *ci calibrate_tsc_freq(); } - tc_init(&tsc_timecounter); + if (tsc_drift_observed > TSC_DRIFT_MAX) { + printf("ERROR: %lld cycle TSC drift observed\n", + (long long)tsc_drift_observed); + tsc_timecounter.tc_quality = -1000; + tsc_is_invariant = 0; + } + + printf("%s: TSC skew=%lld observed drift=%lld\n", __func__, + (long long)ci->ci_tsc_skew, (long long)tsc_drift_observed); + + if (ci->ci_flags & CPUF_PRIMARY) + tc_init(&tsc_timecounter); +} + +/* + * Record drift (in clock cycles). Called during AP startup. + */ +void +tsc_sync_drift(int64_t drift) +{ + if (drift < 0) + drift = -drift; + if (drift > tsc_drift_observed) + tsc_drift_observed = drift; +} + +/* + * Called during startup of APs, by the boot processor. Interrupts + * are disabled on entry. + */ +void +tsc_read_bp(struct cpu_info *ci, uint64_t *bptscp, uint64_t *aptscp) +{ + uint64_t bptsc; + + if (atomic_swap_ptr(&tsc_sync_cpu, ci) != NULL) + panic("tsc_sync_bp: 1"); + + /* Flag it and read our TSC. */ + atomic_setbits_int(&ci->ci_flags, CPUF_SYNCTSC); + bptsc = (rdtsc() >> 1); + + /* Wait for remote to complete, and read ours again. */ + while ((ci->ci_flags & CPUF_SYNCTSC) != 0) + membar_consumer(); + bptsc += (rdtsc() >> 1); + + /* Wait for the results to come in. */ + while (tsc_sync_cpu == ci) + CPU_BUSY_CYCLE(); + if (tsc_sync_cpu != NULL) + panic("tsc_sync_bp: 2"); + + *bptscp = bptsc; + *aptscp = tsc_sync_val; +} + +void +tsc_sync_bp(struct cpu_info *ci) +{ + uint64_t bptsc, aptsc; + + tsc_read_bp(ci, &bptsc, &aptsc); /* discarded - cache effects */ + tsc_read_bp(ci, &bptsc, &aptsc); + + /* Compute final value to adjust for skew. */ + ci->ci_tsc_skew = bptsc - aptsc; +} + +/* + * Called during startup of AP, by the AP itself. Interrupts are + * disabled on entry. + */ +void +tsc_post_ap(struct cpu_info *ci) +{ + uint64_t tsc; + + /* Wait for go-ahead from primary. */ + while ((ci->ci_flags & CPUF_SYNCTSC) == 0) + membar_consumer(); + tsc = (rdtsc() >> 1); + + /* Instruct primary to read its counter. */ + atomic_clearbits_int(&ci->ci_flags, CPUF_SYNCTSC); + tsc += (rdtsc() >> 1); + + /* Post result. Ensure the whole value goes out atomically. */ + (void)atomic_swap_64(&tsc_sync_val, tsc); + + if (atomic_swap_ptr(&tsc_sync_cpu, NULL) != ci) + panic("tsc_sync_ap"); +} + +void +tsc_sync_ap(struct cpu_info *ci) +{ + tsc_post_ap(ci); + tsc_post_ap(ci); } Index: arch/amd64/include/cpu.h =================================================================== RCS file: /cvs/src/sys/arch/amd64/include/cpu.h,v retrieving revision 1.131 diff -u -p -u -p -r1.131 cpu.h --- arch/amd64/include/cpu.h 17 May 2019 19:07:16 -0000 1.131 +++ arch/amd64/include/cpu.h 9 Aug 2019 11:33:41 -0000 @@ -206,6 +206,8 @@ struct cpu_info { union vmm_cpu_cap ci_vmm_cap; paddr_t ci_vmxon_region_pa; struct vmxon_region *ci_vmxon_region; + + int64_t ci_tsc_skew; /* counter skew vs cpu0 */ }; #define CPUF_BSP 0x0001 /* CPU is the original BSP */ @@ -221,6 +223,7 @@ struct cpu_info { #define CPUF_INVAR_TSC 0x0100 /* CPU has invariant TSC */ #define CPUF_USERXSTATE 0x0200 /* CPU has curproc's xsave state */ +#define CPUF_SYNCTSC 0x0800 /* Synchronize TSC */ #define CPUF_PRESENT 0x1000 /* CPU is present */ #define CPUF_RUNNING 0x2000 /* CPU is running */ #define CPUF_PAUSE 0x4000 /* CPU is paused in DDB */ Index: arch/amd64/include/cpuvar.h =================================================================== RCS file: /cvs/src/sys/arch/amd64/include/cpuvar.h,v retrieving revision 1.9 diff -u -p -u -p -r1.9 cpuvar.h --- arch/amd64/include/cpuvar.h 6 Oct 2017 13:33:53 -0000 1.9 +++ arch/amd64/include/cpuvar.h 9 Aug 2019 11:33:41 -0000 @@ -98,4 +98,8 @@ void cpu_init(struct cpu_info *); void cpu_init_first(void); void cpu_adjust_tsc_freq(uint64_t (*)()); +void tsc_sync_drift(int64_t); +void tsc_sync_bp(struct cpu_info *); +void tsc_sync_ap(struct cpu_info *); + #endif