On Thursday 03 January 2008 19:55, Ingo Molnar wrote:
> * Nick Piggin <[EMAIL PROTECTED]> wrote:
> > > Have you done anything more with allowing > 256 CPUS in this
> > > spinlock patch? We've been testing with 1k cpus and to verify with
> > > -mm kernel, we need to "unpatch" these spinlock changes.
> >
> > Hi Mike,
> >
> > Actually I had it in my mind that 64 bit used single-byte locking like
> > i386, so I didn't think I'd caused a regression there.
> >
> > I'll take a look at fixing that up now.
>
> thanks - this is a serious showstopper for the ticket spinlock patch.
>
> ( which has otherwise been performing very well in x86.git so far - it
> has passed a few thousand bootup tests on 64-bit and 32-bit as well,
> so we are close to it being in a mergable state. Would be a pity to
> lose it due to the 256 cpus limit. )
OK, this is what my test harness code looks like for > 256 CPUs
(basically the same as the in-kernel code, but some names etc. are slightly
different).
It passes my basic tests, and performance doesn't seem to have suffered.
I was going to suggest making the <= 256 vs > 256 cases config options, but
maybe we don't need to unless some CPUs are slow at shifts / rotates? I
don't know...
After I get comments, I will come up with an incremental patch against
the kernel... It will be interesting to know whether ticket locks help
big SGI systems.
static inline void xlock(lock_t *lock)
{
lock_t inc = 0x00010000;
lock_t tmp;
__asm__ __volatile__ (
"lock ; xaddl %0, %1\n"
"movzwl %w0, %2\n\t"
"shrl $16, %0\n\t"
"1:\t"
"cmpl %0, %2\n\t"
"je 2f\n\t"
"rep ; nop\n\t"
"movzwl %1, %2\n\t"
/* don't need lfence here, because loads are in-order */
"jmp 1b\n"
"2:"
:"+Q" (inc), "+m" (*lock), "=r" (tmp)
:
:"memory", "cc");
}
static inline int xtrylock(lock_t *lock)
{
lock_t tmp;
lock_t new;
asm volatile(
"movl %2,%0\n\t"
"movl %0,%1\n\t"
"roll $16, %0\n\t"
"cmpl %0,%1\n\t"
"jne 1f\n\t"
"addl $0x00010000, %1\n\t"
"lock ; cmpxchgl %1,%2\n\t"
"1:"
"sete %b1\n\t"
"movzbl %b1,%0\n\t"
:"=&a" (tmp), "=r" (new), "+m" (*lock)
:
: "memory", "cc");
return tmp;
}
static inline void xunlock(lock_t *lock)
{
__asm__ __volatile__(
"incw %0"
:"+m" (*lock)
:
:"memory", "cc");
}
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
