2 * This code largely moved from arch/i386/kernel/timer/timer_tsc.c
3 * which was originally moved from arch/i386/kernel/time.c.
4 * See comments there for proper credits.
7 #include <linux/clocksource.h>
8 #include <linux/workqueue.h>
9 #include <linux/cpufreq.h>
10 #include <linux/jiffies.h>
11 #include <linux/init.h>
12 #include <linux/dmi.h>
14 #include <asm/delay.h>
18 #include "mach_timer.h"
21 * On some systems the TSC frequency does not
22 * change with the cpu frequency. So we need
23 * an extra value to store the TSC freq
26 unsigned long long (*custom_sched_clock
)(void);
31 static int __init
tsc_setup(char *str
)
33 printk(KERN_WARNING
"notsc: Kernel compiled with CONFIG_X86_TSC, "
34 "cannot disable TSC.\n");
39 * disable flag for tsc. Takes effect by clearing the TSC cpu flag
42 static int __init
tsc_setup(char *str
)
50 __setup("notsc", tsc_setup
);
53 * code to mark and check if the TSC is unstable
54 * due to cpufreq or due to unsynced TSCs
56 static int tsc_unstable
;
58 static inline int check_tsc_unstable(void)
63 void mark_tsc_unstable(void)
67 EXPORT_SYMBOL_GPL(mark_tsc_unstable
);
69 /* Accellerators for sched_clock()
70 * convert from cycles(64bits) => nanoseconds (64bits)
72 * ns = cycles / (freq / ns_per_sec)
73 * ns = cycles * (ns_per_sec / freq)
74 * ns = cycles * (10^9 / (cpu_khz * 10^3))
75 * ns = cycles * (10^6 / cpu_khz)
77 * Then we use scaling math (suggested by george@mvista.com) to get:
78 * ns = cycles * (10^6 * SC / cpu_khz) / SC
79 * ns = cycles * cyc2ns_scale / SC
81 * And since SC is a constant power of two, we can convert the div
84 * We can use khz divisor instead of mhz to keep a better percision, since
85 * cyc2ns_scale is limited to 10^6 * 2^10, which fits in 32 bits.
86 * (mathieu.desnoyers@polymtl.ca)
88 * -johnstul@us.ibm.com "math is hard, lets go shopping!"
90 static unsigned long cyc2ns_scale __read_mostly
;
92 #define CYC2NS_SCALE_FACTOR 10 /* 2^10, carefully chosen */
94 static inline void set_cyc2ns_scale(unsigned long cpu_khz
)
96 cyc2ns_scale
= (1000000 << CYC2NS_SCALE_FACTOR
)/cpu_khz
;
99 static inline unsigned long long cycles_2_ns(unsigned long long cyc
)
101 return (cyc
* cyc2ns_scale
) >> CYC2NS_SCALE_FACTOR
;
105 * Scheduler clock - returns current time in nanosec units.
107 unsigned long long sched_clock(void)
109 unsigned long long this_offset
;
111 if (unlikely(custom_sched_clock
))
112 return (*custom_sched_clock
)();
115 * Fall back to jiffies if there's no TSC available:
117 if (unlikely(tsc_disable
))
118 /* No locking but a rare wrong value is not a big deal: */
119 return (jiffies_64
- INITIAL_JIFFIES
) * (1000000000 / HZ
);
121 /* read the Time Stamp Counter: */
122 rdtscll(this_offset
);
124 /* return the value in ns */
125 return cycles_2_ns(this_offset
);
128 static unsigned long calculate_cpu_khz(void)
130 unsigned long long start
, end
;
136 local_irq_save(flags
);
138 /* run 3 times to ensure the cache is warm */
139 for (i
= 0; i
< 3; i
++) {
140 mach_prepare_counter();
142 mach_countup(&count
);
146 * Error: ECTCNEVERSET
147 * The CTC wasn't reliable: we got a hit on the very first read,
148 * or the CPU was so fast/slow that the quotient wouldn't fit in
154 delta64
= end
- start
;
156 /* cpu freq too fast: */
157 if (delta64
> (1ULL<<32))
160 /* cpu freq too slow: */
161 if (delta64
<= CALIBRATE_TIME_MSEC
)
164 delta64
+= CALIBRATE_TIME_MSEC
/2; /* round for do_div */
165 do_div(delta64
,CALIBRATE_TIME_MSEC
);
167 local_irq_restore(flags
);
168 return (unsigned long)delta64
;
170 local_irq_restore(flags
);
174 int recalibrate_cpu_khz(void)
177 unsigned long cpu_khz_old
= cpu_khz
;
180 cpu_khz
= calculate_cpu_khz();
182 cpu_data
[0].loops_per_jiffy
=
183 cpufreq_scale(cpu_data
[0].loops_per_jiffy
,
184 cpu_khz_old
, cpu_khz
);
193 EXPORT_SYMBOL(recalibrate_cpu_khz
);
195 void __init
tsc_init(void)
197 if (!cpu_has_tsc
|| tsc_disable
)
200 cpu_khz
= calculate_cpu_khz();
206 printk("Detected %lu.%03lu MHz processor.\n",
207 (unsigned long)cpu_khz
/ 1000,
208 (unsigned long)cpu_khz
% 1000);
210 set_cyc2ns_scale(cpu_khz
);
216 * Set the tsc_disable flag if there's no TSC support, this
217 * makes it a fast flag for the kernel to see whether it
218 * should be using the TSC.
223 #ifdef CONFIG_CPU_FREQ
226 * if the CPU frequency is scaled, TSC-based delays will need a different
227 * loops_per_jiffy value to function properly.
229 static unsigned int ref_freq
= 0;
230 static unsigned long loops_per_jiffy_ref
= 0;
231 static unsigned long cpu_khz_ref
= 0;
234 time_cpufreq_notifier(struct notifier_block
*nb
, unsigned long val
, void *data
)
236 struct cpufreq_freqs
*freq
= data
;
238 if (val
!= CPUFREQ_RESUMECHANGE
&& val
!= CPUFREQ_SUSPENDCHANGE
)
239 write_seqlock_irq(&xtime_lock
);
243 ref_freq
= freq
->new;
246 ref_freq
= freq
->old
;
247 loops_per_jiffy_ref
= cpu_data
[freq
->cpu
].loops_per_jiffy
;
248 cpu_khz_ref
= cpu_khz
;
251 if ((val
== CPUFREQ_PRECHANGE
&& freq
->old
< freq
->new) ||
252 (val
== CPUFREQ_POSTCHANGE
&& freq
->old
> freq
->new) ||
253 (val
== CPUFREQ_RESUMECHANGE
)) {
254 if (!(freq
->flags
& CPUFREQ_CONST_LOOPS
))
255 cpu_data
[freq
->cpu
].loops_per_jiffy
=
256 cpufreq_scale(loops_per_jiffy_ref
,
257 ref_freq
, freq
->new);
261 if (num_online_cpus() == 1)
262 cpu_khz
= cpufreq_scale(cpu_khz_ref
,
263 ref_freq
, freq
->new);
264 if (!(freq
->flags
& CPUFREQ_CONST_LOOPS
)) {
266 set_cyc2ns_scale(cpu_khz
);
268 * TSC based sched_clock turns
276 if (val
!= CPUFREQ_RESUMECHANGE
&& val
!= CPUFREQ_SUSPENDCHANGE
)
277 write_sequnlock_irq(&xtime_lock
);
282 static struct notifier_block time_cpufreq_notifier_block
= {
283 .notifier_call
= time_cpufreq_notifier
286 static int __init
cpufreq_tsc(void)
288 return cpufreq_register_notifier(&time_cpufreq_notifier_block
,
289 CPUFREQ_TRANSITION_NOTIFIER
);
291 core_initcall(cpufreq_tsc
);
295 /* clock source code */
297 static unsigned long current_tsc_khz
= 0;
298 static int tsc_update_callback(void);
300 static cycle_t
read_tsc(void)
309 static struct clocksource clocksource_tsc
= {
313 .mask
= CLOCKSOURCE_MASK(64),
314 .mult
= 0, /* to be set */
316 .update_callback
= tsc_update_callback
,
320 static int tsc_update_callback(void)
324 /* check to see if we should switch to the safe clocksource: */
325 if (clocksource_tsc
.rating
!= 0 && check_tsc_unstable()) {
326 clocksource_tsc
.rating
= 0;
327 clocksource_reselect();
331 /* only update if tsc_khz has changed: */
332 if (current_tsc_khz
!= tsc_khz
) {
333 current_tsc_khz
= tsc_khz
;
334 clocksource_tsc
.mult
= clocksource_khz2mult(current_tsc_khz
,
335 clocksource_tsc
.shift
);
342 static int __init
dmi_mark_tsc_unstable(struct dmi_system_id
*d
)
344 printk(KERN_NOTICE
"%s detected: marking TSC unstable.\n",
350 /* List of systems that have known TSC problems */
351 static struct dmi_system_id __initdata bad_tsc_dmi_table
[] = {
353 .callback
= dmi_mark_tsc_unstable
,
354 .ident
= "IBM Thinkpad 380XD",
356 DMI_MATCH(DMI_BOARD_VENDOR
, "IBM"),
357 DMI_MATCH(DMI_BOARD_NAME
, "2635FA0"),
363 #define TSC_FREQ_CHECK_INTERVAL (10*MSEC_PER_SEC) /* 10sec in MS */
364 static struct timer_list verify_tsc_freq_timer
;
366 /* XXX - Probably should add locking */
367 static void verify_tsc_freq(unsigned long unused
)
370 static unsigned long last_jiffies
;
372 u64 now_tsc
, interval_tsc
;
373 unsigned long now_jiffies
, interval_jiffies
;
376 if (check_tsc_unstable())
380 now_jiffies
= jiffies
;
386 interval_jiffies
= now_jiffies
- last_jiffies
;
387 interval_tsc
= now_tsc
- last_tsc
;
389 do_div(interval_tsc
, cpu_khz
*1000);
391 if (interval_tsc
< (interval_jiffies
* 3 / 4)) {
392 printk("TSC appears to be running slowly. "
393 "Marking it as unstable\n");
400 last_jiffies
= now_jiffies
;
401 /* set us up to go off on the next interval: */
402 mod_timer(&verify_tsc_freq_timer
,
403 jiffies
+ msecs_to_jiffies(TSC_FREQ_CHECK_INTERVAL
));
407 * Make an educated guess if the TSC is trustworthy and synchronized
410 static __init
int unsynchronized_tsc(void)
413 * Intel systems are normally all synchronized.
414 * Exceptions must mark TSC as unstable:
416 if (boot_cpu_data
.x86_vendor
== X86_VENDOR_INTEL
)
419 /* assume multi socket systems are not synchronized: */
420 return num_possible_cpus() > 1;
423 static int __init
init_tsc_clocksource(void)
426 if (cpu_has_tsc
&& tsc_khz
&& !tsc_disable
) {
427 /* check blacklist */
428 dmi_check_system(bad_tsc_dmi_table
);
430 if (unsynchronized_tsc()) /* mark unstable if unsynced */
432 current_tsc_khz
= tsc_khz
;
433 clocksource_tsc
.mult
= clocksource_khz2mult(current_tsc_khz
,
434 clocksource_tsc
.shift
);
435 /* lower the rating if we already know its unstable: */
436 if (check_tsc_unstable())
437 clocksource_tsc
.rating
= 0;
439 init_timer(&verify_tsc_freq_timer
);
440 verify_tsc_freq_timer
.function
= verify_tsc_freq
;
441 verify_tsc_freq_timer
.expires
=
442 jiffies
+ msecs_to_jiffies(TSC_FREQ_CHECK_INTERVAL
);
443 add_timer(&verify_tsc_freq_timer
);
445 return clocksource_register(&clocksource_tsc
);
451 module_init(init_tsc_clocksource
);