Merge branches 'x86/apic', 'x86/cleanups', 'x86/cpufeature', 'x86/crashdump', 'x86...
[linux-2.6.git] / arch / x86 / kernel / tsc_sync.c
1 /*
2  * check TSC synchronization.
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
49         rdtsc_barrier();
50         start = get_cycles();
51         rdtsc_barrier();
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;
66                 rdtsc_barrier();
67                 now = get_cycles();
68                 rdtsc_barrier();
69                 last_tsc = now;
70                 __raw_spin_unlock(&sync_lock);
71
72                 /*
73                  * Be nice every now and then (and also check whether
74                  * measurement is done [we also insert a 10 million
75                  * loops safety exit, so we dont lock up in case the
76                  * TSC readout is totally broken]):
77                  */
78                 if (unlikely(!(i & 7))) {
79                         if (now > end || i > 10000000)
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                 }
94         }
95         WARN(!(now-start),
96                 "Warning: zero tsc calibration delta: %Ld [max: %Ld]\n",
97                         now-start, end-start);
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         if (boot_cpu_has(X86_FEATURE_TSC_RELIABLE)) {
116                 printk(KERN_INFO
117                        "Skipping synchronization checks as TSC is reliable.\n");
118                 return;
119         }
120
121         printk(KERN_INFO "checking TSC synchronization [CPU#%d -> CPU#%d]:",
122                           smp_processor_id(), cpu);
123
124         /*
125          * Reset it - in case this is a second bootup:
126          */
127         atomic_set(&stop_count, 0);
128
129         /*
130          * Wait for the target to arrive:
131          */
132         while (atomic_read(&start_count) != cpus-1)
133                 cpu_relax();
134         /*
135          * Trigger the target to continue into the measurement too:
136          */
137         atomic_inc(&start_count);
138
139         check_tsc_warp();
140
141         while (atomic_read(&stop_count) != cpus-1)
142                 cpu_relax();
143
144         if (nr_warps) {
145                 printk("\n");
146                 printk(KERN_WARNING "Measured %Ld cycles TSC warp between CPUs,"
147                                     " turning off TSC clock.\n", max_warp);
148                 mark_tsc_unstable("check_tsc_sync_source failed");
149         } else {
150                 printk(" passed.\n");
151         }
152
153         /*
154          * Reset it - just in case we boot another CPU later:
155          */
156         atomic_set(&start_count, 0);
157         nr_warps = 0;
158         max_warp = 0;
159         last_tsc = 0;
160
161         /*
162          * Let the target continue with the bootup:
163          */
164         atomic_inc(&stop_count);
165 }
166
167 /*
168  * Freshly booted CPUs call into this:
169  */
170 void __cpuinit check_tsc_sync_target(void)
171 {
172         int cpus = 2;
173
174         if (unsynchronized_tsc() || boot_cpu_has(X86_FEATURE_TSC_RELIABLE))
175                 return;
176
177         /*
178          * Register this CPU's participation and wait for the
179          * source CPU to start the measurement:
180          */
181         atomic_inc(&start_count);
182         while (atomic_read(&start_count) != cpus)
183                 cpu_relax();
184
185         check_tsc_warp();
186
187         /*
188          * Ok, we are done:
189          */
190         atomic_inc(&stop_count);
191
192         /*
193          * Wait for the source CPU to print stuff:
194          */
195         while (atomic_read(&stop_count) != cpus)
196                 cpu_relax();
197 }
198 #undef NR_LOOPS
199