Commit 8c071b0f authored by Martin Schwidefsky's avatar Martin Schwidefsky
Browse files

s390/time: correct use of store clock fast 



The result of the store-clock-fast (STCKF) instruction is a bit fuzzy.
It can happen that the value stored on one CPU is smaller than the value
stored on another CPU, although the order of the stores is the other
way around. This can cause deltas of get_tod_clock() values to become
negative when they should not be.

We need to be more careful with store-clock-fast, this patch partially
reverts git commit e4b7b4238e666682555461fa52eecd74652f36bb "time:
always use stckf instead of stck if available". The get_tod_clock()
function now uses the store-clock-extended (STCKE) instruction.
get_tod_clock_fast() can be used if the fuzziness of store-clock-fast
is acceptable e.g. for wait loops local to a CPU.

Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
parent 9784bd4f

arch/s390/include/asm/timex.h

+14 −14
Original line number Diff line number Diff line
@@ -71,30 +71,30 @@ static inline void local_tick_enable(unsigned long long comp) 


typedef unsigned long long cycles_t;



static inline unsigned long long get_tod_clock(void)

{

	unsigned long long clk;



#ifdef CONFIG_HAVE_MARCH_Z9_109_FEATURES

	asm volatile(".insn s,0xb27c0000,%0" : "=Q" (clk) : : "cc");

#else

	asm volatile("stck %0" : "=Q" (clk) : : "cc");

#endif

	return clk;

}



static inline void get_tod_clock_ext(char *clk)

{

	asm volatile("stcke %0" : "=Q" (*clk) : : "cc");

}



static inline unsigned long long get_tod_clock_xt(void)

static inline unsigned long long get_tod_clock(void)

{

	unsigned char clk[16];

	get_tod_clock_ext(clk);

	return *((unsigned long long *)&clk[1]);

}



static inline unsigned long long get_tod_clock_fast(void)

{

#ifdef CONFIG_HAVE_MARCH_Z9_109_FEATURES

	unsigned long long clk;



	asm volatile("stckf %0" : "=Q" (clk) : : "cc");

	return clk;

#else

	return get_tod_clock();

#endif

}



static inline cycles_t get_cycles(void)

{

	return (cycles_t) get_tod_clock() >> 2;
@@ -125,7 +125,7 @@ extern u64 sched_clock_base_cc; 
 */

static inline unsigned long long get_tod_clock_monotonic(void)

{

	return get_tod_clock_xt() - sched_clock_base_cc;

	return get_tod_clock() - sched_clock_base_cc;

}



/**

arch/s390/kernel/debug.c

+1 −1
Original line number Diff line number Diff line
@@ -867,7 +867,7 @@ static inline void 
debug_finish_entry(debug_info_t * id, debug_entry_t* active, int level,

			int exception)

{

	active->id.stck = get_tod_clock();

	active->id.stck = get_tod_clock_fast();

	active->id.fields.cpuid = smp_processor_id();

	active->caller = __builtin_return_address(0);

	active->id.fields.exception = exception;

arch/s390/kvm/interrupt.c

+3 −3
Original line number Diff line number Diff line
@@ -385,7 +385,7 @@ static int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu) 
	}



	if ((!rc) && (vcpu->arch.sie_block->ckc <

		get_tod_clock() + vcpu->arch.sie_block->epoch)) {

		get_tod_clock_fast() + vcpu->arch.sie_block->epoch)) {

		if ((!psw_extint_disabled(vcpu)) &&

			(vcpu->arch.sie_block->gcr[0] & 0x800ul))

			rc = 1;
@@ -425,7 +425,7 @@ int kvm_s390_handle_wait(struct kvm_vcpu *vcpu) 
		goto no_timer;

	}



	now = get_tod_clock() + vcpu->arch.sie_block->epoch;

	now = get_tod_clock_fast() + vcpu->arch.sie_block->epoch;

	if (vcpu->arch.sie_block->ckc < now) {

		__unset_cpu_idle(vcpu);

		return 0;
@@ -515,7 +515,7 @@ void kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu) 
	}



	if ((vcpu->arch.sie_block->ckc <

		get_tod_clock() + vcpu->arch.sie_block->epoch))

		get_tod_clock_fast() + vcpu->arch.sie_block->epoch))

		__try_deliver_ckc_interrupt(vcpu);



	if (atomic_read(&fi->active)) {

arch/s390/lib/delay.c

+7 −7
Original line number Diff line number Diff line
@@ -44,7 +44,7 @@ static void __udelay_disabled(unsigned long long usecs) 
	do {

		set_clock_comparator(end);

		vtime_stop_cpu();

	} while (get_tod_clock() < end);

	} while (get_tod_clock_fast() < end);

	lockdep_on();

	__ctl_load(cr0, 0, 0);

	__ctl_load(cr6, 6, 6);
@@ -55,7 +55,7 @@ static void __udelay_enabled(unsigned long long usecs) 
{

	u64 clock_saved, end;



	end = get_tod_clock() + (usecs << 12);

	end = get_tod_clock_fast() + (usecs << 12);

	do {

		clock_saved = 0;

		if (end < S390_lowcore.clock_comparator) {
@@ -65,7 +65,7 @@ static void __udelay_enabled(unsigned long long usecs) 
		vtime_stop_cpu();

		if (clock_saved)

			local_tick_enable(clock_saved);

	} while (get_tod_clock() < end);

	} while (get_tod_clock_fast() < end);

}



/*
@@ -109,8 +109,8 @@ void udelay_simple(unsigned long long usecs) 
{

	u64 end;



	end = get_tod_clock() + (usecs << 12);

	while (get_tod_clock() < end)

	end = get_tod_clock_fast() + (usecs << 12);

	while (get_tod_clock_fast() < end)

		cpu_relax();

}
@@ -120,10 +120,10 @@ void __ndelay(unsigned long long nsecs) 


	nsecs <<= 9;

	do_div(nsecs, 125);

	end = get_tod_clock() + nsecs;

	end = get_tod_clock_fast() + nsecs;

	if (nsecs & ~0xfffUL)

		__udelay(nsecs >> 12);

	while (get_tod_clock() < end)

	while (get_tod_clock_fast() < end)

		barrier();

}

EXPORT_SYMBOL(__ndelay);

drivers/s390/char/sclp.c

+2 −2
Original line number Diff line number Diff line
@@ -486,7 +486,7 @@ sclp_sync_wait(void) 
	timeout = 0;

	if (timer_pending(&sclp_request_timer)) {

		/* Get timeout TOD value */

		timeout = get_tod_clock() +

		timeout = get_tod_clock_fast() +

			  sclp_tod_from_jiffies(sclp_request_timer.expires -

						jiffies);

	}
@@ -508,7 +508,7 @@ sclp_sync_wait(void) 
	while (sclp_running_state != sclp_running_state_idle) {

		/* Check for expired request timer */

		if (timer_pending(&sclp_request_timer) &&

		    get_tod_clock() > timeout &&

		    get_tod_clock_fast() > timeout &&

		    del_timer(&sclp_request_timer))

			sclp_request_timer.function(sclp_request_timer.data);

		cpu_relax();

CRA Git | Maintained and supported by SUSTech CRA and CCSE