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Commit | Line | Data |
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250c2277 | 1 | /* |
835c34a1 | 2 | * check TSC synchronization. |
250c2277 TG |
3 | * |
4 | * Copyright (C) 2006, Red Hat, Inc., Ingo Molnar | |
5 | * | |
6 | * We check whether all boot CPUs have their TSC's synchronized, | |
7 | * print a warning if not and turn off the TSC clock-source. | |
8 | * | |
9 | * The warp-check is point-to-point between two CPUs, the CPU | |
10 | * initiating the bootup is the 'source CPU', the freshly booting | |
11 | * CPU is the 'target CPU'. | |
12 | * | |
13 | * Only two CPUs may participate - they can enter in any order. | |
14 | * ( The serial nature of the boot logic and the CPU hotplug lock | |
15 | * protects against more than 2 CPUs entering this code. ) | |
16 | */ | |
17 | #include <linux/spinlock.h> | |
18 | #include <linux/kernel.h> | |
19 | #include <linux/init.h> | |
20 | #include <linux/smp.h> | |
21 | #include <linux/nmi.h> | |
22 | #include <asm/tsc.h> | |
23 | ||
24 | /* | |
25 | * Entry/exit counters that make sure that both CPUs | |
26 | * run the measurement code at once: | |
27 | */ | |
28 | static __cpuinitdata atomic_t start_count; | |
29 | static __cpuinitdata atomic_t stop_count; | |
30 | ||
31 | /* | |
32 | * We use a raw spinlock in this exceptional case, because | |
33 | * we want to have the fastest, inlined, non-debug version | |
34 | * of a critical section, to be able to prove TSC time-warps: | |
35 | */ | |
36 | static __cpuinitdata raw_spinlock_t sync_lock = __RAW_SPIN_LOCK_UNLOCKED; | |
37 | static __cpuinitdata cycles_t last_tsc; | |
38 | static __cpuinitdata cycles_t max_warp; | |
39 | static __cpuinitdata int nr_warps; | |
40 | ||
41 | /* | |
42 | * TSC-warp measurement loop running on both CPUs: | |
43 | */ | |
44 | static __cpuinit void check_tsc_warp(void) | |
45 | { | |
46 | cycles_t start, now, prev, end; | |
47 | int i; | |
48 | ||
93ce99e8 | 49 | rdtsc_barrier(); |
6d63de8d | 50 | start = get_cycles(); |
93ce99e8 | 51 | rdtsc_barrier(); |
250c2277 TG |
52 | /* |
53 | * The measurement runs for 20 msecs: | |
54 | */ | |
55 | end = start + tsc_khz * 20ULL; | |
56 | now = start; | |
57 | ||
58 | for (i = 0; ; i++) { | |
59 | /* | |
60 | * We take the global lock, measure TSC, save the | |
61 | * previous TSC that was measured (possibly on | |
62 | * another CPU) and update the previous TSC timestamp. | |
63 | */ | |
64 | __raw_spin_lock(&sync_lock); | |
65 | prev = last_tsc; | |
93ce99e8 | 66 | rdtsc_barrier(); |
6d63de8d | 67 | now = get_cycles(); |
93ce99e8 | 68 | rdtsc_barrier(); |
250c2277 TG |
69 | last_tsc = now; |
70 | __raw_spin_unlock(&sync_lock); | |
71 | ||
72 | /* | |
73 | * Be nice every now and then (and also check whether | |
df43510b | 74 | * measurement is done [we also insert a 10 million |
250c2277 TG |
75 | * loops safety exit, so we dont lock up in case the |
76 | * TSC readout is totally broken]): | |
77 | */ | |
78 | if (unlikely(!(i & 7))) { | |
df43510b | 79 | if (now > end || i > 10000000) |
250c2277 TG |
80 | break; |
81 | cpu_relax(); | |
82 | touch_nmi_watchdog(); | |
83 | } | |
84 | /* | |
85 | * Outside the critical section we can now see whether | |
86 | * we saw a time-warp of the TSC going backwards: | |
87 | */ | |
88 | if (unlikely(prev > now)) { | |
89 | __raw_spin_lock(&sync_lock); | |
90 | max_warp = max(max_warp, prev - now); | |
91 | nr_warps++; | |
92 | __raw_spin_unlock(&sync_lock); | |
93 | } | |
ad8ca495 | 94 | } |
bde78a79 AV |
95 | WARN(!(now-start), |
96 | "Warning: zero tsc calibration delta: %Ld [max: %Ld]\n", | |
ad8ca495 | 97 | now-start, end-start); |
250c2277 TG |
98 | } |
99 | ||
100 | /* | |
101 | * Source CPU calls into this - it waits for the freshly booted | |
102 | * target CPU to arrive and then starts the measurement: | |
103 | */ | |
104 | void __cpuinit check_tsc_sync_source(int cpu) | |
105 | { | |
106 | int cpus = 2; | |
107 | ||
108 | /* | |
109 | * No need to check if we already know that the TSC is not | |
110 | * synchronized: | |
111 | */ | |
112 | if (unsynchronized_tsc()) | |
113 | return; | |
114 | ||
115 | printk(KERN_INFO "checking TSC synchronization [CPU#%d -> CPU#%d]:", | |
116 | smp_processor_id(), cpu); | |
117 | ||
118 | /* | |
119 | * Reset it - in case this is a second bootup: | |
120 | */ | |
121 | atomic_set(&stop_count, 0); | |
122 | ||
123 | /* | |
124 | * Wait for the target to arrive: | |
125 | */ | |
126 | while (atomic_read(&start_count) != cpus-1) | |
127 | cpu_relax(); | |
128 | /* | |
129 | * Trigger the target to continue into the measurement too: | |
130 | */ | |
131 | atomic_inc(&start_count); | |
132 | ||
133 | check_tsc_warp(); | |
134 | ||
135 | while (atomic_read(&stop_count) != cpus-1) | |
136 | cpu_relax(); | |
137 | ||
250c2277 TG |
138 | if (nr_warps) { |
139 | printk("\n"); | |
140 | printk(KERN_WARNING "Measured %Ld cycles TSC warp between CPUs," | |
141 | " turning off TSC clock.\n", max_warp); | |
142 | mark_tsc_unstable("check_tsc_sync_source failed"); | |
250c2277 TG |
143 | } else { |
144 | printk(" passed.\n"); | |
145 | } | |
146 | ||
4c6b8b4d MG |
147 | /* |
148 | * Reset it - just in case we boot another CPU later: | |
149 | */ | |
150 | atomic_set(&start_count, 0); | |
151 | nr_warps = 0; | |
152 | max_warp = 0; | |
153 | last_tsc = 0; | |
154 | ||
250c2277 TG |
155 | /* |
156 | * Let the target continue with the bootup: | |
157 | */ | |
158 | atomic_inc(&stop_count); | |
159 | } | |
160 | ||
161 | /* | |
162 | * Freshly booted CPUs call into this: | |
163 | */ | |
164 | void __cpuinit check_tsc_sync_target(void) | |
165 | { | |
166 | int cpus = 2; | |
167 | ||
168 | if (unsynchronized_tsc()) | |
169 | return; | |
170 | ||
171 | /* | |
172 | * Register this CPU's participation and wait for the | |
173 | * source CPU to start the measurement: | |
174 | */ | |
175 | atomic_inc(&start_count); | |
176 | while (atomic_read(&start_count) != cpus) | |
177 | cpu_relax(); | |
178 | ||
179 | check_tsc_warp(); | |
180 | ||
181 | /* | |
182 | * Ok, we are done: | |
183 | */ | |
184 | atomic_inc(&stop_count); | |
185 | ||
186 | /* | |
187 | * Wait for the source CPU to print stuff: | |
188 | */ | |
189 | while (atomic_read(&stop_count) != cpus) | |
190 | cpu_relax(); | |
191 | } | |
192 | #undef NR_LOOPS | |
193 |