Linux 2.6.25.3

[linux/fpc-iii.git] / arch / x86 / oprofile / op_model_p4.c

/**
 * @file op_model_p4.c
 * P4 model-specific MSR operations
 *
 * @remark Copyright 2002 OProfile authors
 * @remark Read the file COPYING
 *
 * @author Graydon Hoare
 */

#include <linux/oprofile.h>
#include <linux/smp.h>
#include <asm/msr.h>
#include <asm/ptrace.h>
#include <asm/fixmap.h>
#include <asm/apic.h>
#include <asm/nmi.h>

#include "op_x86_model.h"
#include "op_counter.h"

#define NUM_EVENTS 39

#define NUM_COUNTERS_NON_HT 8
#define NUM_ESCRS_NON_HT 45
#define NUM_CCCRS_NON_HT 18
#define NUM_CONTROLS_NON_HT (NUM_ESCRS_NON_HT + NUM_CCCRS_NON_HT)

#define NUM_COUNTERS_HT2 4
#define NUM_ESCRS_HT2 23
#define NUM_CCCRS_HT2 9
#define NUM_CONTROLS_HT2 (NUM_ESCRS_HT2 + NUM_CCCRS_HT2)

static unsigned int num_counters = NUM_COUNTERS_NON_HT;
static unsigned int num_controls = NUM_CONTROLS_NON_HT;

/* this has to be checked dynamically since the
   hyper-threadedness of a chip is discovered at
   kernel boot-time. */
static inline void setup_num_counters(void)
{
#ifdef CONFIG_SMP
        if (smp_num_siblings == 2){
                num_counters = NUM_COUNTERS_HT2;
                num_controls = NUM_CONTROLS_HT2;
        }
#endif
}

static int inline addr_increment(void)
{
#ifdef CONFIG_SMP
        return smp_num_siblings == 2 ? 2 : 1;
#else
        return 1;
#endif
}


/* tables to simulate simplified hardware view of p4 registers */
struct p4_counter_binding {
        int virt_counter;
        int counter_address;
        int cccr_address;
};

struct p4_event_binding {
        int escr_select;  /* value to put in CCCR */
        int event_select; /* value to put in ESCR */
        struct {
                int virt_counter; /* for this counter... */
                int escr_address; /* use this ESCR       */
        } bindings[2];
};

/* nb: these CTR_* defines are a duplicate of defines in
   event/i386.p4*events. */


#define CTR_BPU_0      (1 << 0)
#define CTR_MS_0       (1 << 1)
#define CTR_FLAME_0    (1 << 2)
#define CTR_IQ_4       (1 << 3)
#define CTR_BPU_2      (1 << 4)
#define CTR_MS_2       (1 << 5)
#define CTR_FLAME_2    (1 << 6)
#define CTR_IQ_5       (1 << 7)

static struct p4_counter_binding p4_counters [NUM_COUNTERS_NON_HT] = {
        { CTR_BPU_0,   MSR_P4_BPU_PERFCTR0,   MSR_P4_BPU_CCCR0 },
        { CTR_MS_0,    MSR_P4_MS_PERFCTR0,    MSR_P4_MS_CCCR0 },
        { CTR_FLAME_0, MSR_P4_FLAME_PERFCTR0, MSR_P4_FLAME_CCCR0 },
        { CTR_IQ_4,    MSR_P4_IQ_PERFCTR4,    MSR_P4_IQ_CCCR4 },
        { CTR_BPU_2,   MSR_P4_BPU_PERFCTR2,   MSR_P4_BPU_CCCR2 },
        { CTR_MS_2,    MSR_P4_MS_PERFCTR2,    MSR_P4_MS_CCCR2 },
        { CTR_FLAME_2, MSR_P4_FLAME_PERFCTR2, MSR_P4_FLAME_CCCR2 },
        { CTR_IQ_5,    MSR_P4_IQ_PERFCTR5,    MSR_P4_IQ_CCCR5 }
};

#define NUM_UNUSED_CCCRS        NUM_CCCRS_NON_HT - NUM_COUNTERS_NON_HT

/* p4 event codes in libop/op_event.h are indices into this table. */

static struct p4_event_binding p4_events[NUM_EVENTS] = {
        
        { /* BRANCH_RETIRED */
                0x05, 0x06, 
                { {CTR_IQ_4, MSR_P4_CRU_ESCR2},
                  {CTR_IQ_5, MSR_P4_CRU_ESCR3} }
        },
        
        { /* MISPRED_BRANCH_RETIRED */
                0x04, 0x03, 
                { { CTR_IQ_4, MSR_P4_CRU_ESCR0},
                  { CTR_IQ_5, MSR_P4_CRU_ESCR1} }
        },
        
        { /* TC_DELIVER_MODE */
                0x01, 0x01,
                { { CTR_MS_0, MSR_P4_TC_ESCR0},  
                  { CTR_MS_2, MSR_P4_TC_ESCR1} }
        },
        
        { /* BPU_FETCH_REQUEST */
                0x00, 0x03, 
                { { CTR_BPU_0, MSR_P4_BPU_ESCR0},
                  { CTR_BPU_2, MSR_P4_BPU_ESCR1} }
        },

        { /* ITLB_REFERENCE */
                0x03, 0x18,
                { { CTR_BPU_0, MSR_P4_ITLB_ESCR0},
                  { CTR_BPU_2, MSR_P4_ITLB_ESCR1} }
        },

        { /* MEMORY_CANCEL */
                0x05, 0x02,
                { { CTR_FLAME_0, MSR_P4_DAC_ESCR0},
                  { CTR_FLAME_2, MSR_P4_DAC_ESCR1} }
        },

        { /* MEMORY_COMPLETE */
                0x02, 0x08,
                { { CTR_FLAME_0, MSR_P4_SAAT_ESCR0},
                  { CTR_FLAME_2, MSR_P4_SAAT_ESCR1} }
        },

        { /* LOAD_PORT_REPLAY */
                0x02, 0x04, 
                { { CTR_FLAME_0, MSR_P4_SAAT_ESCR0},
                  { CTR_FLAME_2, MSR_P4_SAAT_ESCR1} }
        },

        { /* STORE_PORT_REPLAY */
                0x02, 0x05,
                { { CTR_FLAME_0, MSR_P4_SAAT_ESCR0},
                  { CTR_FLAME_2, MSR_P4_SAAT_ESCR1} }
        },

        { /* MOB_LOAD_REPLAY */
                0x02, 0x03,
                { { CTR_BPU_0, MSR_P4_MOB_ESCR0},
                  { CTR_BPU_2, MSR_P4_MOB_ESCR1} }
        },

        { /* PAGE_WALK_TYPE */
                0x04, 0x01,
                { { CTR_BPU_0, MSR_P4_PMH_ESCR0},
                  { CTR_BPU_2, MSR_P4_PMH_ESCR1} }
        },

        { /* BSQ_CACHE_REFERENCE */
                0x07, 0x0c, 
                { { CTR_BPU_0, MSR_P4_BSU_ESCR0},
                  { CTR_BPU_2, MSR_P4_BSU_ESCR1} }
        },

        { /* IOQ_ALLOCATION */
                0x06, 0x03, 
                { { CTR_BPU_0, MSR_P4_FSB_ESCR0},
                  { 0, 0 } }
        },

        { /* IOQ_ACTIVE_ENTRIES */
                0x06, 0x1a, 
                { { CTR_BPU_2, MSR_P4_FSB_ESCR1},
                  { 0, 0 } }
        },

        { /* FSB_DATA_ACTIVITY */
                0x06, 0x17, 
                { { CTR_BPU_0, MSR_P4_FSB_ESCR0},
                  { CTR_BPU_2, MSR_P4_FSB_ESCR1} }
        },

        { /* BSQ_ALLOCATION */
                0x07, 0x05, 
                { { CTR_BPU_0, MSR_P4_BSU_ESCR0},
                  { 0, 0 } }
        },

        { /* BSQ_ACTIVE_ENTRIES */
                0x07, 0x06,
                { { CTR_BPU_2, MSR_P4_BSU_ESCR1 /* guess */},  
                  { 0, 0 } }
        },

        { /* X87_ASSIST */
                0x05, 0x03, 
                { { CTR_IQ_4, MSR_P4_CRU_ESCR2},
                  { CTR_IQ_5, MSR_P4_CRU_ESCR3} }
        },

        { /* SSE_INPUT_ASSIST */
                0x01, 0x34,
                { { CTR_FLAME_0, MSR_P4_FIRM_ESCR0},
                  { CTR_FLAME_2, MSR_P4_FIRM_ESCR1} }
        },
  
        { /* PACKED_SP_UOP */
                0x01, 0x08, 
                { { CTR_FLAME_0, MSR_P4_FIRM_ESCR0},
                  { CTR_FLAME_2, MSR_P4_FIRM_ESCR1} }
        },
  
        { /* PACKED_DP_UOP */
                0x01, 0x0c, 
                { { CTR_FLAME_0, MSR_P4_FIRM_ESCR0},
                  { CTR_FLAME_2, MSR_P4_FIRM_ESCR1} }
        },

        { /* SCALAR_SP_UOP */
                0x01, 0x0a, 
                { { CTR_FLAME_0, MSR_P4_FIRM_ESCR0},
                  { CTR_FLAME_2, MSR_P4_FIRM_ESCR1} }
        },

        { /* SCALAR_DP_UOP */
                0x01, 0x0e,
                { { CTR_FLAME_0, MSR_P4_FIRM_ESCR0},
                  { CTR_FLAME_2, MSR_P4_FIRM_ESCR1} }
        },

        { /* 64BIT_MMX_UOP */
                0x01, 0x02, 
                { { CTR_FLAME_0, MSR_P4_FIRM_ESCR0},
                  { CTR_FLAME_2, MSR_P4_FIRM_ESCR1} }
        },
  
        { /* 128BIT_MMX_UOP */
                0x01, 0x1a, 
                { { CTR_FLAME_0, MSR_P4_FIRM_ESCR0},
                  { CTR_FLAME_2, MSR_P4_FIRM_ESCR1} }
        },

        { /* X87_FP_UOP */
                0x01, 0x04, 
                { { CTR_FLAME_0, MSR_P4_FIRM_ESCR0},
                  { CTR_FLAME_2, MSR_P4_FIRM_ESCR1} }
        },
  
        { /* X87_SIMD_MOVES_UOP */
                0x01, 0x2e, 
                { { CTR_FLAME_0, MSR_P4_FIRM_ESCR0},
                  { CTR_FLAME_2, MSR_P4_FIRM_ESCR1} }
        },
  
        { /* MACHINE_CLEAR */
                0x05, 0x02, 
                { { CTR_IQ_4, MSR_P4_CRU_ESCR2},
                  { CTR_IQ_5, MSR_P4_CRU_ESCR3} }
        },

        { /* GLOBAL_POWER_EVENTS */
                0x06, 0x13 /* older manual says 0x05, newer 0x13 */,
                { { CTR_BPU_0, MSR_P4_FSB_ESCR0},
                  { CTR_BPU_2, MSR_P4_FSB_ESCR1} }
        },
  
        { /* TC_MS_XFER */
                0x00, 0x05, 
                { { CTR_MS_0, MSR_P4_MS_ESCR0},
                  { CTR_MS_2, MSR_P4_MS_ESCR1} }
        },

        { /* UOP_QUEUE_WRITES */
                0x00, 0x09,
                { { CTR_MS_0, MSR_P4_MS_ESCR0},
                  { CTR_MS_2, MSR_P4_MS_ESCR1} }
        },

        { /* FRONT_END_EVENT */
                0x05, 0x08,
                { { CTR_IQ_4, MSR_P4_CRU_ESCR2},
                  { CTR_IQ_5, MSR_P4_CRU_ESCR3} }
        },

        { /* EXECUTION_EVENT */
                0x05, 0x0c,
                { { CTR_IQ_4, MSR_P4_CRU_ESCR2},
                  { CTR_IQ_5, MSR_P4_CRU_ESCR3} }
        },

        { /* REPLAY_EVENT */
                0x05, 0x09,
                { { CTR_IQ_4, MSR_P4_CRU_ESCR2},
                  { CTR_IQ_5, MSR_P4_CRU_ESCR3} }
        },

        { /* INSTR_RETIRED */
                0x04, 0x02, 
                { { CTR_IQ_4, MSR_P4_CRU_ESCR0},
                  { CTR_IQ_5, MSR_P4_CRU_ESCR1} }
        },

        { /* UOPS_RETIRED */
                0x04, 0x01,
                { { CTR_IQ_4, MSR_P4_CRU_ESCR0},
                  { CTR_IQ_5, MSR_P4_CRU_ESCR1} }
        },

        { /* UOP_TYPE */    
                0x02, 0x02, 
                { { CTR_IQ_4, MSR_P4_RAT_ESCR0},
                  { CTR_IQ_5, MSR_P4_RAT_ESCR1} }
        },

        { /* RETIRED_MISPRED_BRANCH_TYPE */
                0x02, 0x05, 
                { { CTR_MS_0, MSR_P4_TBPU_ESCR0},
                  { CTR_MS_2, MSR_P4_TBPU_ESCR1} }
        },

        { /* RETIRED_BRANCH_TYPE */
                0x02, 0x04,
                { { CTR_MS_0, MSR_P4_TBPU_ESCR0},
                  { CTR_MS_2, MSR_P4_TBPU_ESCR1} }
        }
};


#define MISC_PMC_ENABLED_P(x) ((x) & 1 << 7)

#define ESCR_RESERVED_BITS 0x80000003
#define ESCR_CLEAR(escr) ((escr) &= ESCR_RESERVED_BITS)
#define ESCR_SET_USR_0(escr, usr) ((escr) |= (((usr) & 1) << 2))
#define ESCR_SET_OS_0(escr, os) ((escr) |= (((os) & 1) << 3))
#define ESCR_SET_USR_1(escr, usr) ((escr) |= (((usr) & 1)))
#define ESCR_SET_OS_1(escr, os) ((escr) |= (((os) & 1) << 1))
#define ESCR_SET_EVENT_SELECT(escr, sel) ((escr) |= (((sel) & 0x3f) << 25))
#define ESCR_SET_EVENT_MASK(escr, mask) ((escr) |= (((mask) & 0xffff) << 9))
#define ESCR_READ(escr,high,ev,i) do {rdmsr(ev->bindings[(i)].escr_address, (escr), (high));} while (0)
#define ESCR_WRITE(escr,high,ev,i) do {wrmsr(ev->bindings[(i)].escr_address, (escr), (high));} while (0)

#define CCCR_RESERVED_BITS 0x38030FFF
#define CCCR_CLEAR(cccr) ((cccr) &= CCCR_RESERVED_BITS)
#define CCCR_SET_REQUIRED_BITS(cccr) ((cccr) |= 0x00030000)
#define CCCR_SET_ESCR_SELECT(cccr, sel) ((cccr) |= (((sel) & 0x07) << 13))
#define CCCR_SET_PMI_OVF_0(cccr) ((cccr) |= (1<<26))
#define CCCR_SET_PMI_OVF_1(cccr) ((cccr) |= (1<<27))
#define CCCR_SET_ENABLE(cccr) ((cccr) |= (1<<12))
#define CCCR_SET_DISABLE(cccr) ((cccr) &= ~(1<<12))
#define CCCR_READ(low, high, i) do {rdmsr(p4_counters[(i)].cccr_address, (low), (high));} while (0)
#define CCCR_WRITE(low, high, i) do {wrmsr(p4_counters[(i)].cccr_address, (low), (high));} while (0)
#define CCCR_OVF_P(cccr) ((cccr) & (1U<<31))
#define CCCR_CLEAR_OVF(cccr) ((cccr) &= (~(1U<<31)))

#define CTRL_IS_RESERVED(msrs,c) (msrs->controls[(c)].addr ? 1 : 0)
#define CTR_IS_RESERVED(msrs,c) (msrs->counters[(c)].addr ? 1 : 0)
#define CTR_READ(l,h,i) do {rdmsr(p4_counters[(i)].counter_address, (l), (h));} while (0)
#define CTR_WRITE(l,i) do {wrmsr(p4_counters[(i)].counter_address, -(u32)(l), -1);} while (0)
#define CTR_OVERFLOW_P(ctr) (!((ctr) & 0x80000000))


/* this assigns a "stagger" to the current CPU, which is used throughout
   the code in this module as an extra array offset, to select the "even"
   or "odd" part of all the divided resources. */
static unsigned int get_stagger(void)
{
#ifdef CONFIG_SMP
        int cpu = smp_processor_id();
        return (cpu != first_cpu(per_cpu(cpu_sibling_map, cpu)));
#endif  
        return 0;
}


/* finally, mediate access to a real hardware counter
   by passing a "virtual" counter numer to this macro,
   along with your stagger setting. */
#define VIRT_CTR(stagger, i) ((i) + ((num_counters) * (stagger)))

static unsigned long reset_value[NUM_COUNTERS_NON_HT];


static void p4_fill_in_addresses(struct op_msrs * const msrs)
{
        unsigned int i; 
        unsigned int addr, cccraddr, stag;

        setup_num_counters();
        stag = get_stagger();

        /* initialize some registers */
        for (i = 0; i < num_counters; ++i) {
                msrs->counters[i].addr = 0;
        }
        for (i = 0; i < num_controls; ++i) {
                msrs->controls[i].addr = 0;
        }
        
        /* the counter & cccr registers we pay attention to */
        for (i = 0; i < num_counters; ++i) {
                addr = p4_counters[VIRT_CTR(stag, i)].counter_address;
                cccraddr = p4_counters[VIRT_CTR(stag, i)].cccr_address;
                if (reserve_perfctr_nmi(addr)){
                        msrs->counters[i].addr = addr;
                        msrs->controls[i].addr = cccraddr;
                }
        }

        /* 43 ESCR registers in three or four discontiguous group */
        for (addr = MSR_P4_BSU_ESCR0 + stag;
             addr < MSR_P4_IQ_ESCR0; ++i, addr += addr_increment()) {
                if (reserve_evntsel_nmi(addr))
                        msrs->controls[i].addr = addr;
        }

        /* no IQ_ESCR0/1 on some models, we save a seconde time BSU_ESCR0/1
         * to avoid special case in nmi_{save|restore}_registers() */
        if (boot_cpu_data.x86_model >= 0x3) {
                for (addr = MSR_P4_BSU_ESCR0 + stag;
                     addr <= MSR_P4_BSU_ESCR1; ++i, addr += addr_increment()) {
                        if (reserve_evntsel_nmi(addr))
                                msrs->controls[i].addr = addr;
                }
        } else {
                for (addr = MSR_P4_IQ_ESCR0 + stag;
                     addr <= MSR_P4_IQ_ESCR1; ++i, addr += addr_increment()) {
                        if (reserve_evntsel_nmi(addr))
                                msrs->controls[i].addr = addr;
                }
        }

        for (addr = MSR_P4_RAT_ESCR0 + stag;
             addr <= MSR_P4_SSU_ESCR0; ++i, addr += addr_increment()) {
                if (reserve_evntsel_nmi(addr))
                        msrs->controls[i].addr = addr;
        }
        
        for (addr = MSR_P4_MS_ESCR0 + stag;
             addr <= MSR_P4_TC_ESCR1; ++i, addr += addr_increment()) { 
                if (reserve_evntsel_nmi(addr))
                        msrs->controls[i].addr = addr;
        }
        
        for (addr = MSR_P4_IX_ESCR0 + stag;
             addr <= MSR_P4_CRU_ESCR3; ++i, addr += addr_increment()) { 
                if (reserve_evntsel_nmi(addr))
                        msrs->controls[i].addr = addr;
        }

        /* there are 2 remaining non-contiguously located ESCRs */

        if (num_counters == NUM_COUNTERS_NON_HT) {              
                /* standard non-HT CPUs handle both remaining ESCRs*/
                if (reserve_evntsel_nmi(MSR_P4_CRU_ESCR5))
                        msrs->controls[i++].addr = MSR_P4_CRU_ESCR5;
                if (reserve_evntsel_nmi(MSR_P4_CRU_ESCR4))
                        msrs->controls[i++].addr = MSR_P4_CRU_ESCR4;

        } else if (stag == 0) {
                /* HT CPUs give the first remainder to the even thread, as
                   the 32nd control register */
                if (reserve_evntsel_nmi(MSR_P4_CRU_ESCR4))
                        msrs->controls[i++].addr = MSR_P4_CRU_ESCR4;

        } else {
                /* and two copies of the second to the odd thread,
                   for the 22st and 23nd control registers */
                if (reserve_evntsel_nmi(MSR_P4_CRU_ESCR5)) {
                        msrs->controls[i++].addr = MSR_P4_CRU_ESCR5;
                        msrs->controls[i++].addr = MSR_P4_CRU_ESCR5;
                }
        }
}


static void pmc_setup_one_p4_counter(unsigned int ctr)
{
        int i;
        int const maxbind = 2;
        unsigned int cccr = 0;
        unsigned int escr = 0;
        unsigned int high = 0;
        unsigned int counter_bit;
        struct p4_event_binding *ev = NULL;
        unsigned int stag;

        stag = get_stagger();
        
        /* convert from counter *number* to counter *bit* */
        counter_bit = 1 << VIRT_CTR(stag, ctr);
        
        /* find our event binding structure. */
        if (counter_config[ctr].event <= 0 || counter_config[ctr].event > NUM_EVENTS) {
                printk(KERN_ERR 
                       "oprofile: P4 event code 0x%lx out of range\n", 
                       counter_config[ctr].event);
                return;
        }
        
        ev = &(p4_events[counter_config[ctr].event - 1]);
        
        for (i = 0; i < maxbind; i++) {
                if (ev->bindings[i].virt_counter & counter_bit) {

                        /* modify ESCR */
                        ESCR_READ(escr, high, ev, i);
                        ESCR_CLEAR(escr);
                        if (stag == 0) {
                                ESCR_SET_USR_0(escr, counter_config[ctr].user);
                                ESCR_SET_OS_0(escr, counter_config[ctr].kernel);
                        } else {
                                ESCR_SET_USR_1(escr, counter_config[ctr].user);
                                ESCR_SET_OS_1(escr, counter_config[ctr].kernel);
                        }
                        ESCR_SET_EVENT_SELECT(escr, ev->event_select);
                        ESCR_SET_EVENT_MASK(escr, counter_config[ctr].unit_mask);                       
                        ESCR_WRITE(escr, high, ev, i);
                       
                        /* modify CCCR */
                        CCCR_READ(cccr, high, VIRT_CTR(stag, ctr));
                        CCCR_CLEAR(cccr);
                        CCCR_SET_REQUIRED_BITS(cccr);
                        CCCR_SET_ESCR_SELECT(cccr, ev->escr_select);
                        if (stag == 0) {
                                CCCR_SET_PMI_OVF_0(cccr);
                        } else {
                                CCCR_SET_PMI_OVF_1(cccr);
                        }
                        CCCR_WRITE(cccr, high, VIRT_CTR(stag, ctr));
                        return;
                }
        }

        printk(KERN_ERR 
               "oprofile: P4 event code 0x%lx no binding, stag %d ctr %d\n",
               counter_config[ctr].event, stag, ctr);
}


static void p4_setup_ctrs(struct op_msrs const * const msrs)
{
        unsigned int i;
        unsigned int low, high;
        unsigned int stag;

        stag = get_stagger();

        rdmsr(MSR_IA32_MISC_ENABLE, low, high);
        if (! MISC_PMC_ENABLED_P(low)) {
                printk(KERN_ERR "oprofile: P4 PMC not available\n");
                return;
        }

        /* clear the cccrs we will use */
        for (i = 0 ; i < num_counters ; i++) {
                if (unlikely(!CTRL_IS_RESERVED(msrs,i)))
                        continue;
                rdmsr(p4_counters[VIRT_CTR(stag, i)].cccr_address, low, high);
                CCCR_CLEAR(low);
                CCCR_SET_REQUIRED_BITS(low);
                wrmsr(p4_counters[VIRT_CTR(stag, i)].cccr_address, low, high);
        }

        /* clear all escrs (including those outside our concern) */
        for (i = num_counters; i < num_controls; i++) {
                if (unlikely(!CTRL_IS_RESERVED(msrs,i)))
                        continue;
                wrmsr(msrs->controls[i].addr, 0, 0);
        }

        /* setup all counters */
        for (i = 0 ; i < num_counters ; ++i) {
                if ((counter_config[i].enabled) && (CTRL_IS_RESERVED(msrs,i))) {
                        reset_value[i] = counter_config[i].count;
                        pmc_setup_one_p4_counter(i);
                        CTR_WRITE(counter_config[i].count, VIRT_CTR(stag, i));
                } else {
                        reset_value[i] = 0;
                }
        }
}


static int p4_check_ctrs(struct pt_regs * const regs,
                         struct op_msrs const * const msrs)
{
        unsigned long ctr, low, high, stag, real;
        int i;

        stag = get_stagger();

        for (i = 0; i < num_counters; ++i) {
                
                if (!reset_value[i]) 
                        continue;

                /* 
                 * there is some eccentricity in the hardware which
                 * requires that we perform 2 extra corrections:
                 *
                 * - check both the CCCR:OVF flag for overflow and the
                 *   counter high bit for un-flagged overflows.
                 *
                 * - write the counter back twice to ensure it gets
                 *   updated properly.
                 * 
                 * the former seems to be related to extra NMIs happening
                 * during the current NMI; the latter is reported as errata
                 * N15 in intel doc 249199-029, pentium 4 specification
                 * update, though their suggested work-around does not
                 * appear to solve the problem.
                 */
                
                real = VIRT_CTR(stag, i);

                CCCR_READ(low, high, real);
                CTR_READ(ctr, high, real);
                if (CCCR_OVF_P(low) || CTR_OVERFLOW_P(ctr)) {
                        oprofile_add_sample(regs, i);
                        CTR_WRITE(reset_value[i], real);
                        CCCR_CLEAR_OVF(low);
                        CCCR_WRITE(low, high, real);
                        CTR_WRITE(reset_value[i], real);
                }
        }

        /* P4 quirk: you have to re-unmask the apic vector */
        apic_write(APIC_LVTPC, apic_read(APIC_LVTPC) & ~APIC_LVT_MASKED);

        /* See op_model_ppro.c */
        return 1;
}


static void p4_start(struct op_msrs const * const msrs)
{
        unsigned int low, high, stag;
        int i;

        stag = get_stagger();

        for (i = 0; i < num_counters; ++i) {
                if (!reset_value[i])
                        continue;
                CCCR_READ(low, high, VIRT_CTR(stag, i));
                CCCR_SET_ENABLE(low);
                CCCR_WRITE(low, high, VIRT_CTR(stag, i));
        }
}


static void p4_stop(struct op_msrs const * const msrs)
{
        unsigned int low, high, stag;
        int i;

        stag = get_stagger();

        for (i = 0; i < num_counters; ++i) {
                if (!reset_value[i])
                        continue;
                CCCR_READ(low, high, VIRT_CTR(stag, i));
                CCCR_SET_DISABLE(low);
                CCCR_WRITE(low, high, VIRT_CTR(stag, i));
        }
}

static void p4_shutdown(struct op_msrs const * const msrs)
{
        int i;

        for (i = 0 ; i < num_counters ; ++i) {
                if (CTR_IS_RESERVED(msrs,i))
                        release_perfctr_nmi(msrs->counters[i].addr);
        }
        /* some of the control registers are specially reserved in
         * conjunction with the counter registers (hence the starting offset).
         * This saves a few bits.
         */
        for (i = num_counters ; i < num_controls ; ++i) {
                if (CTRL_IS_RESERVED(msrs,i))
                        release_evntsel_nmi(msrs->controls[i].addr);
        }
}


#ifdef CONFIG_SMP
struct op_x86_model_spec const op_p4_ht2_spec = {
        .num_counters = NUM_COUNTERS_HT2,
        .num_controls = NUM_CONTROLS_HT2,
        .fill_in_addresses = &p4_fill_in_addresses,
        .setup_ctrs = &p4_setup_ctrs,
        .check_ctrs = &p4_check_ctrs,
        .start = &p4_start,
        .stop = &p4_stop,
        .shutdown = &p4_shutdown
};
#endif

struct op_x86_model_spec const op_p4_spec = {
        .num_counters = NUM_COUNTERS_NON_HT,
        .num_controls = NUM_CONTROLS_NON_HT,
        .fill_in_addresses = &p4_fill_in_addresses,
        .setup_ctrs = &p4_setup_ctrs,
        .check_ctrs = &p4_check_ctrs,
        .start = &p4_start,
        .stop = &p4_stop,
        .shutdown = &p4_shutdown
};