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Commit c35a7261 authored by Andrew Morton's avatar Andrew Morton Committed by Linus Torvalds
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[PATCH] synchronize_tsc() fixes 



- Move the tsc synchronisation variables into a struct, mark it __initdata

- local `realdelta' wants to be 64-bit

- Print the skew for negative skews, as well as for positive ones

- remove dead code

Cc: john stultz <johnstul@us.ibm.com>
Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
parent 851f8a69

arch/i386/kernel/smpboot.c

+33 −29
Original line number Diff line number Diff line
@@ -212,10 +212,16 @@ valid_k7: 
 * then we print a warning if not, and always resync.

 */



static atomic_t tsc_start_flag = ATOMIC_INIT(0);

static atomic_t tsc_count_start = ATOMIC_INIT(0);

static atomic_t tsc_count_stop = ATOMIC_INIT(0);

static unsigned long long tsc_values[NR_CPUS];

static struct {

	atomic_t start_flag;

	atomic_t count_start;

	atomic_t count_stop;

	unsigned long long values[NR_CPUS];

} tsc __initdata = {

	.start_flag = ATOMIC_INIT(0),

	.count_start = ATOMIC_INIT(0),

	.count_stop = ATOMIC_INIT(0),

};



#define NR_LOOPS 5
@@ -233,7 +239,7 @@ static void __init synchronize_tsc_bp (void) 
	/* convert from kcyc/sec to cyc/usec */

	one_usec = cpu_khz / 1000;



	atomic_set(&tsc_start_flag, 1);

	atomic_set(&tsc.start_flag, 1);

	wmb();



	/*
@@ -250,16 +256,16 @@ static void __init synchronize_tsc_bp (void) 
		/*

		 * all APs synchronize but they loop on '== num_cpus'

		 */

		while (atomic_read(&tsc_count_start) != num_booting_cpus()-1)

		while (atomic_read(&tsc.count_start) != num_booting_cpus()-1)

			cpu_relax();

		atomic_set(&tsc_count_stop, 0);

		atomic_set(&tsc.count_stop, 0);

		wmb();

		/*

		 * this lets the APs save their current TSC:

		 */

		atomic_inc(&tsc_count_start);

		atomic_inc(&tsc.count_start);



		rdtscll(tsc_values[smp_processor_id()]);

		rdtscll(tsc.values[smp_processor_id()]);

		/*

		 * We clear the TSC in the last loop:

		 */
@@ -269,50 +275,48 @@ static void __init synchronize_tsc_bp (void) 
		/*

		 * Wait for all APs to leave the synchronization point:

		 */

		while (atomic_read(&tsc_count_stop) != num_booting_cpus()-1)

		while (atomic_read(&tsc.count_stop) != num_booting_cpus()-1)

			cpu_relax();

		atomic_set(&tsc_count_start, 0);

		atomic_set(&tsc.count_start, 0);

		wmb();

		atomic_inc(&tsc_count_stop);

		atomic_inc(&tsc.count_stop);

	}



	sum = 0;

	for (i = 0; i < NR_CPUS; i++) {

		if (cpu_isset(i, cpu_callout_map)) {

			t0 = tsc_values[i];

			t0 = tsc.values[i];

			sum += t0;

		}

	}

	avg = sum;

	do_div(avg, num_booting_cpus());



	sum = 0;

	for (i = 0; i < NR_CPUS; i++) {

		if (!cpu_isset(i, cpu_callout_map))

			continue;

		delta = tsc_values[i] - avg;

		delta = tsc.values[i] - avg;

		if (delta < 0)

			delta = -delta;

		/*

		 * We report bigger than 2 microseconds clock differences.

		 */

		if (delta > 2*one_usec) {

			long realdelta;

			long long realdelta;



			if (!buggy) {

				buggy = 1;

				printk("\n");

			}

			realdelta = delta;

			do_div(realdelta, one_usec);

			if (tsc_values[i] < avg)

			if (tsc.values[i] < avg)

				realdelta = -realdelta;



			if (realdelta > 0)

				printk(KERN_INFO "CPU#%d had %ld usecs TSC "

			if (realdelta)

				printk(KERN_INFO "CPU#%d had %Ld usecs TSC "

					"skew, fixed it up.\n", i, realdelta);

		}



		sum += delta;

	}

	if (!buggy)

		printk("passed.\n");
@@ -327,20 +331,20 @@ static void __init synchronize_tsc_ap (void) 
	 * this gets called, so we first wait for the BP to

	 * finish SMP initialization:

	 */

	while (!atomic_read(&tsc_start_flag))

	while (!atomic_read(&tsc.start_flag))

		cpu_relax();



	for (i = 0; i < NR_LOOPS; i++) {

		atomic_inc(&tsc_count_start);

		while (atomic_read(&tsc_count_start) != num_booting_cpus())

		atomic_inc(&tsc.count_start);

		while (atomic_read(&tsc.count_start) != num_booting_cpus())

			cpu_relax();



		rdtscll(tsc_values[smp_processor_id()]);

		rdtscll(tsc.values[smp_processor_id()]);

		if (i == NR_LOOPS-1)

			write_tsc(0, 0);



		atomic_inc(&tsc_count_stop);

		while (atomic_read(&tsc_count_stop) != num_booting_cpus())

		atomic_inc(&tsc.count_stop);

		while (atomic_read(&tsc.count_stop) != num_booting_cpus())

			cpu_relax();

	}

}