parisc: Optimize timer interrupt function

Restructure the timer interrupt function to better cope with missed timer irqs.
Optimize the calculation when the next interrupt should happen and skip irqs if
they would happen too shortly after exit of the irq function.

The update_process_times() call is done anyway at every timer irq, so we can
safely drop the prof_counter and prof_multiplier variables from the per_cpu
structure.

Signed-off-by: Helge Deller <deller@gmx.de>

arch/parisc/include/asm/processor.h

@@ -93,9 +93,7 @@ struct system_cpuinfo_parisc {
 /* Per CPU data structure - ie varies per CPU.  */
 struct cpuinfo_parisc {
 	unsigned long it_value;     /* Interval Timer at last timer Intr */
-	unsigned long it_delta;     /* Interval delta (tic_10ms / HZ * 100) */
 	unsigned long irq_count;    /* number of IRQ's since boot */
-	unsigned long irq_max_cr16; /* longest time to handle a single IRQ */
 	unsigned long cpuid;        /* aka slot_number or set to NO_PROC_ID */
 	unsigned long hpa;          /* Host Physical address */
 	unsigned long txn_addr;     /* MMIO addr of EIR or id_eid */
@@ -103,8 +101,6 @@ struct cpuinfo_parisc {
 	unsigned long pending_ipi;  /* bitmap of type ipi_message_type */
 #endif
 	unsigned long bh_count;     /* number of times bh was invoked */
-	unsigned long prof_counter; /* per CPU profiling support */
-	unsigned long prof_multiplier;	/* per CPU profiling support */
 	unsigned long fp_rev;
 	unsigned long fp_model;
 	unsigned int state;