RE: [git pull] ia64 changes

Luck, Tony
2009-09-28T22:35:27Z

Here are the source and disassembled binary for the lock/unlock
routines modified as suggested by Linus to fit the lock word
back into 32-bits.

Performance for lock/unlock time in the uncontended in-cache case
is a little worse (another 8% on top of the 8% I'd already given
up compared to the original "xchg" version). I haven't tried a
macro-level benchmark yet to see whether this makes it noticeable.

-Tony

#define TICKET_SHIFT 17
#define TICKET_BITS 15

static __always_inline void __ticket_spin_lock(raw_spinlock_t *lock)
{
int *p = (int *)&lock->lock, ticket, serve;

ticket = ia64_fetchadd(1, p, acq);

if (!(((ticket >> TICKET_SHIFT) ^ ticket) & ((1L << TICKET_BITS) - 1)))
return;

do {
cpu_relax();
serve = ACCESS_ONCE(*p);
} while (((serve >> TICKET_SHIFT) ^ ticket) & ((1 << TICKET_BITS) - 1));
}

a000000100815d00 <_spin_lock>:
a000000100815d00: [MII] fetchadd4.acq r14=[r32],1
a000000100815d06: nop.i 0x0
a000000100815d0c: nop.i 0x0;;
a000000100815d10: [MII] nop.m 0x0
a000000100815d16: extr r3=r14,17,15
a000000100815d1c: mov r172767
a000000100815d20: [MMI] mov r16=r14;;
a000000100815d26: xor r2=r14,r3
a000000100815d2c: nop.i 0x0;;
a000000100815d30: [MII] nop.m 0x0
a000000100815d36: extr.u r15=r2,0,15;;
a000000100815d3c: nop.i 0x0
a000000100815d40: [MMB] cmp.eq p6,p7=0,r15
a000000100815d46: nop.m 0x0
a000000100815d4c: (p06) br.ret.dpnt.many b0
a000000100815d50: [MMI] hint.m 0x0
a000000100815d56: nop.m 0x0
a000000100815d5c: nop.i 0x0;;
a000000100815d60: [MMI] ld4.acq r11=[r32];;
a000000100815d66: nop.m 0x0
a000000100815d6c: extr r10=r11,17,15;;
a000000100815d70: [MMI] xor r9=r16,r10;;
a000000100815d76: and r8=r17,r9
a000000100815d7c: nop.i 0x0;;
a000000100815d80: [MIB] nop.m 0x0
a000000100815d86: cmp4.eq p9,p8=0,r8
a000000100815d8c: (p08) br.cond.dptk.few a000000100815d50 <_spin_lock+0x50>
a000000100815d90: [MIB] nop.m 0x0
a000000100815d96: nop.i 0x0
a000000100815d9c: br.ret.sptk.many b0;;

static __always_inline void __ticket_spin_unlock(raw_spinlock_t *lock)
{
unsigned short *p = (unsigned short *)&lock->lock + 1, tmp;

asm volatile ("ld2.bias %0=[%1]" : "=r"(tmp) : "r"(p));
ACCESS_ONCE(*p) = (tmp + 2) & ~1;
}

a00000010000a4a0: [MII] mov r36e534
...
a00000010000a4d0: [MII] ld2.bias r9=[r34]
a00000010000a4d6: nop.i 0x0
a00000010000a4dc: nop.i 0x0;;
a00000010000a4e0: [MMI] adds r8=2,r9;;
a00000010000a4e6: and r3=r36,r8
a00000010000a4ec: nop.i 0x0
a00000010000a4f0: [MMI] nop.m 0x0;;
a00000010000a4f6: st2.rel [r34]=r3