diff options
Diffstat (limited to 'arch/x86/kernel/tsc_sync.c')
| -rw-r--r-- | arch/x86/kernel/tsc_sync.c | 290 |
1 files changed, 277 insertions, 13 deletions
diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c index 78083bf23ed1..d0db011051a5 100644 --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -14,18 +14,166 @@ * ( The serial nature of the boot logic and the CPU hotplug lock * protects against more than 2 CPUs entering this code. ) */ +#include <linux/topology.h> #include <linux/spinlock.h> #include <linux/kernel.h> #include <linux/smp.h> #include <linux/nmi.h> #include <asm/tsc.h> +struct tsc_adjust { + s64 bootval; + s64 adjusted; + unsigned long nextcheck; + bool warned; +}; + +static DEFINE_PER_CPU(struct tsc_adjust, tsc_adjust); + +void tsc_verify_tsc_adjust(bool resume) +{ + struct tsc_adjust *adj = this_cpu_ptr(&tsc_adjust); + s64 curval; + + if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST)) + return; + + /* Rate limit the MSR check */ + if (!resume && time_before(jiffies, adj->nextcheck)) + return; + + adj->nextcheck = jiffies + HZ; + + rdmsrl(MSR_IA32_TSC_ADJUST, curval); + if (adj->adjusted == curval) + return; + + /* Restore the original value */ + wrmsrl(MSR_IA32_TSC_ADJUST, adj->adjusted); + + if (!adj->warned || resume) { + pr_warn(FW_BUG "TSC ADJUST differs: CPU%u %lld --> %lld. Restoring\n", + smp_processor_id(), adj->adjusted, curval); + adj->warned = true; + } +} + +static void tsc_sanitize_first_cpu(struct tsc_adjust *cur, s64 bootval, + unsigned int cpu, bool bootcpu) +{ + /* + * First online CPU in a package stores the boot value in the + * adjustment value. This value might change later via the sync + * mechanism. If that fails we still can yell about boot values not + * being consistent. + * + * On the boot cpu we just force set the ADJUST value to 0 if it's + * non zero. We don't do that on non boot cpus because physical + * hotplug should have set the ADJUST register to a value > 0 so + * the TSC is in sync with the already running cpus. + * + * But we always force positive ADJUST values. Otherwise the TSC + * deadline timer creates an interrupt storm. We also have to + * prevent values > 0x7FFFFFFF as those wreckage the timer as well. + */ + if ((bootcpu && bootval != 0) || (!bootcpu && bootval < 0) || + (bootval > 0x7FFFFFFF)) { + pr_warn(FW_BUG "TSC ADJUST: CPU%u: %lld force to 0\n", cpu, + bootval); + wrmsrl(MSR_IA32_TSC_ADJUST, 0); + bootval = 0; + } + cur->adjusted = bootval; +} + +#ifndef CONFIG_SMP +bool __init tsc_store_and_check_tsc_adjust(bool bootcpu) +{ + struct tsc_adjust *cur = this_cpu_ptr(&tsc_adjust); + s64 bootval; + + if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST)) + return false; + + rdmsrl(MSR_IA32_TSC_ADJUST, bootval); + cur->bootval = bootval; + cur->nextcheck = jiffies + HZ; + tsc_sanitize_first_cpu(cur, bootval, smp_processor_id(), bootcpu); + return false; +} + +#else /* !CONFIG_SMP */ + +/* + * Store and check the TSC ADJUST MSR if available + */ +bool tsc_store_and_check_tsc_adjust(bool bootcpu) +{ + struct tsc_adjust *ref, *cur = this_cpu_ptr(&tsc_adjust); + unsigned int refcpu, cpu = smp_processor_id(); + struct cpumask *mask; + s64 bootval; + + if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST)) + return false; + + rdmsrl(MSR_IA32_TSC_ADJUST, bootval); + cur->bootval = bootval; + cur->nextcheck = jiffies + HZ; + cur->warned = false; + + /* + * Check whether this CPU is the first in a package to come up. In + * this case do not check the boot value against another package + * because the new package might have been physically hotplugged, + * where TSC_ADJUST is expected to be different. When called on the + * boot CPU topology_core_cpumask() might not be available yet. + */ + mask = topology_core_cpumask(cpu); + refcpu = mask ? cpumask_any_but(mask, cpu) : nr_cpu_ids; + + if (refcpu >= nr_cpu_ids) { + tsc_sanitize_first_cpu(cur, bootval, smp_processor_id(), + bootcpu); + return false; + } + + ref = per_cpu_ptr(&tsc_adjust, refcpu); + /* + * Compare the boot value and complain if it differs in the + * package. + */ + if (bootval != ref->bootval) { + pr_warn(FW_BUG "TSC ADJUST differs: Reference CPU%u: %lld CPU%u: %lld\n", + refcpu, ref->bootval, cpu, bootval); + } + /* + * The TSC_ADJUST values in a package must be the same. If the boot + * value on this newly upcoming CPU differs from the adjustment + * value of the already online CPU in this package, set it to that + * adjusted value. + */ + if (bootval != ref->adjusted) { + pr_warn("TSC ADJUST synchronize: Reference CPU%u: %lld CPU%u: %lld\n", + refcpu, ref->adjusted, cpu, bootval); + cur->adjusted = ref->adjusted; + wrmsrl(MSR_IA32_TSC_ADJUST, ref->adjusted); + } + /* + * We have the TSCs forced to be in sync on this package. Skip sync + * test: + */ + return true; +} + /* * Entry/exit counters that make sure that both CPUs * run the measurement code at once: */ static atomic_t start_count; static atomic_t stop_count; +static atomic_t skip_test; +static atomic_t test_runs; /* * We use a raw spinlock in this exceptional case, because @@ -37,15 +185,16 @@ static arch_spinlock_t sync_lock = __ARCH_SPIN_LOCK_UNLOCKED; static cycles_t last_tsc; static cycles_t max_warp; static int nr_warps; +static int random_warps; /* * TSC-warp measurement loop running on both CPUs. This is not called * if there is no TSC. */ -static void check_tsc_warp(unsigned int timeout) +static cycles_t check_tsc_warp(unsigned int timeout) { - cycles_t start, now, prev, end; - int i; + cycles_t start, now, prev, end, cur_max_warp = 0; + int i, cur_warps = 0; start = rdtsc_ordered(); /* @@ -85,13 +234,22 @@ static void check_tsc_warp(unsigned int timeout) if (unlikely(prev > now)) { arch_spin_lock(&sync_lock); max_warp = max(max_warp, prev - now); + cur_max_warp = max_warp; + /* + * Check whether this bounces back and forth. Only + * one CPU should observe time going backwards. + */ + if (cur_warps != nr_warps) + random_warps++; nr_warps++; + cur_warps = nr_warps; arch_spin_unlock(&sync_lock); } } WARN(!(now-start), "Warning: zero tsc calibration delta: %Ld [max: %Ld]\n", now-start, end-start); + return cur_max_warp; } /* @@ -136,15 +294,26 @@ void check_tsc_sync_source(int cpu) } /* - * Reset it - in case this is a second bootup: + * Set the maximum number of test runs to + * 1 if the CPU does not provide the TSC_ADJUST MSR + * 3 if the MSR is available, so the target can try to adjust */ - atomic_set(&stop_count, 0); - + if (!boot_cpu_has(X86_FEATURE_TSC_ADJUST)) + atomic_set(&test_runs, 1); + else + atomic_set(&test_runs, 3); +retry: /* - * Wait for the target to arrive: + * Wait for the target to start or to skip the test: */ - while (atomic_read(&start_count) != cpus-1) + while (atomic_read(&start_count) != cpus - 1) { + if (atomic_read(&skip_test) > 0) { + atomic_set(&skip_test, 0); + return; + } cpu_relax(); + } + /* * Trigger the target to continue into the measurement too: */ @@ -155,21 +324,35 @@ void check_tsc_sync_source(int cpu) while (atomic_read(&stop_count) != cpus-1) cpu_relax(); - if (nr_warps) { + /* + * If the test was successful set the number of runs to zero and + * stop. If not, decrement the number of runs an check if we can + * retry. In case of random warps no retry is attempted. + */ + if (!nr_warps) { + atomic_set(&test_runs, 0); + + pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n", + smp_processor_id(), cpu); + + } else if (atomic_dec_and_test(&test_runs) || random_warps) { + /* Force it to 0 if random warps brought us here */ + atomic_set(&test_runs, 0); + pr_warning("TSC synchronization [CPU#%d -> CPU#%d]:\n", smp_processor_id(), cpu); pr_warning("Measured %Ld cycles TSC warp between CPUs, " "turning off TSC clock.\n", max_warp); + if (random_warps) + pr_warning("TSC warped randomly between CPUs\n"); mark_tsc_unstable("check_tsc_sync_source failed"); - } else { - pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n", - smp_processor_id(), cpu); } /* * Reset it - just in case we boot another CPU later: */ atomic_set(&start_count, 0); + random_warps = 0; nr_warps = 0; max_warp = 0; last_tsc = 0; @@ -178,6 +361,12 @@ void check_tsc_sync_source(int cpu) * Let the target continue with the bootup: */ atomic_inc(&stop_count); + + /* + * Retry, if there is a chance to do so. + */ + if (atomic_read(&test_runs) > 0) + goto retry; } /* @@ -185,6 +374,9 @@ void check_tsc_sync_source(int cpu) */ void check_tsc_sync_target(void) { + struct tsc_adjust *cur = this_cpu_ptr(&tsc_adjust); + unsigned int cpu = smp_processor_id(); + cycles_t cur_max_warp, gbl_max_warp; int cpus = 2; /* Also aborts if there is no TSC. */ @@ -192,6 +384,16 @@ void check_tsc_sync_target(void) return; /* + * Store, verify and sanitize the TSC adjust register. If + * successful skip the test. + */ + if (tsc_store_and_check_tsc_adjust(false)) { + atomic_inc(&skip_test); + return; + } + +retry: + /* * Register this CPU's participation and wait for the * source CPU to start the measurement: */ @@ -199,7 +401,12 @@ void check_tsc_sync_target(void) while (atomic_read(&start_count) != cpus) cpu_relax(); - check_tsc_warp(loop_timeout(smp_processor_id())); + cur_max_warp = check_tsc_warp(loop_timeout(cpu)); + + /* + * Store the maximum observed warp value for a potential retry: + */ + gbl_max_warp = max_warp; /* * Ok, we are done: @@ -211,4 +418,61 @@ void check_tsc_sync_target(void) */ while (atomic_read(&stop_count) != cpus) cpu_relax(); + + /* + * Reset it for the next sync test: + */ + atomic_set(&stop_count, 0); + + /* + * Check the number of remaining test runs. If not zero, the test + * failed and a retry with adjusted TSC is possible. If zero the + * test was either successful or failed terminally. + */ + if (!atomic_read(&test_runs)) + return; + + /* + * If the warp value of this CPU is 0, then the other CPU + * observed time going backwards so this TSC was ahead and + * needs to move backwards. + */ + if (!cur_max_warp) + cur_max_warp = -gbl_max_warp; + + /* + * Add the result to the previous adjustment value. + * + * The adjustement value is slightly off by the overhead of the + * sync mechanism (observed values are ~200 TSC cycles), but this + * really depends on CPU, node distance and frequency. So + * compensating for this is hard to get right. Experiments show + * that the warp is not longer detectable when the observed warp + * value is used. In the worst case the adjustment needs to go + * through a 3rd run for fine tuning. + */ + cur->adjusted += cur_max_warp; + + /* + * TSC deadline timer stops working or creates an interrupt storm + * with adjust values < 0 and > x07ffffff. + * + * To allow adjust values > 0x7FFFFFFF we need to disable the + * deadline timer and use the local APIC timer, but that requires + * more intrusive changes and we do not have any useful information + * from Intel about the underlying HW wreckage yet. + */ + if (cur->adjusted < 0) + cur->adjusted = 0; + if (cur->adjusted > 0x7FFFFFFF) + cur->adjusted = 0x7FFFFFFF; + + pr_warn("TSC ADJUST compensate: CPU%u observed %lld warp. Adjust: %lld\n", + cpu, cur_max_warp, cur->adjusted); + + wrmsrl(MSR_IA32_TSC_ADJUST, cur->adjusted); + goto retry; + } + +#endif /* CONFIG_SMP */ |