On 02.09.2015 22:29, Helge Deller wrote:
> parisc: Align locks for LWS syscalls to L1 cache size (v2)
>
> Align the locks for the Light-weight-syscall (LWS) which are used
> for atomic userspace operations (e.g. gcc atomic builtins) on L1 cache
> boundaries. This should speed up LWS calls on PA20 systems.
>
> Reported-by: John David Anglin <dave.anglin@xxxxxxxx>
> Signed-off-by: Helge Deller <deller@xxxxxx>
Any objections to this patch ?
One idea below...
>
> diff --git a/arch/parisc/kernel/syscall.S b/arch/parisc/kernel/syscall.S
> index 7ef22e3..80c2306 100644
> --- a/arch/parisc/kernel/syscall.S
> +++ b/arch/parisc/kernel/syscall.S
> @@ -561,9 +561,9 @@ lws_compare_and_swap:
> extru %r26, 27, 4, %r20
>
> /* Find lock to use, the hash is either one of 0 to
> - 15, multiplied by 16 (keep it 16-byte aligned)
> + 15, multiplied by L1_CACHE_BYTES (keep it L1 cache aligned)
> and add to the lock table offset. */
> - shlw %r20, 4, %r20
> + shlw %r20, L1_CACHE_SHIFT, %r20
> add %r20, %r28, %r20
>
> # if ENABLE_LWS_DEBUG
> @@ -751,9 +751,9 @@ cas2_lock_start:
> extru %r26, 27, 4, %r20
>
> /* Find lock to use, the hash is either one of 0 to
> - 15, multiplied by 16 (keep it 16-byte aligned)
> + 15, multiplied by L1_CACHE_BYTES (keep it L1 cache aligned)
> and add to the lock table offset. */
> - shlw %r20, 4, %r20
> + shlw %r20, L1_CACHE_SHIFT, %r20
> add %r20, %r28, %r20
>
> rsm PSW_SM_I, %r0 /* Disable interrupts */
> @@ -931,11 +931,9 @@ END(sys_call_table64)
> ENTRY(lws_lock_start)
> /* lws locks */
> .rept 16
> - /* Keep locks aligned at 16-bytes */
> + /* Keep locks aligned to L1_CACHE_BYTES */
> .word 1
> - .word 0
> - .word 0
> - .word 0
> + .align L1_CACHE_BYTES
> .endr
I think this alignment/increase of each array entry to size of L1_CACHE_BYTES
should be limited to the SMP case only... For UP 16 bytes would be ok.
Helge
> END(lws_lock_start)
> .previous
>
>
> diff --git a/arch/parisc/include/asm/futex.h b/arch/parisc/include/asm/futex.h
> index 49df148..47b075c 100644
> --- a/arch/parisc/include/asm/futex.h
> +++ b/arch/parisc/include/asm/futex.h
> @@ -15,7 +15,7 @@ static inline void
> _futex_spin_lock_irqsave(u32 __user *uaddr, unsigned long int *flags)
> {
> extern u32 lws_lock_start[];
> - long index = ((long)uaddr & 0xf0) >> 2;
> + long index = (((long)uaddr & 0xf0) >> 4) << (L1_CACHE_SHIFT-2);
> arch_spinlock_t *s = (arch_spinlock_t *)&lws_lock_start[index];
> local_irq_save(*flags);
> arch_spin_lock(s);
> @@ -25,7 +25,7 @@ static inline void
> _futex_spin_unlock_irqrestore(u32 __user *uaddr, unsigned long int *flags)
> {
> extern u32 lws_lock_start[];
> - long index = ((long)uaddr & 0xf0) >> 2;
> + long index = (((long)uaddr & 0xf0) >> 4) << (L1_CACHE_SHIFT-2);
> arch_spinlock_t *s = (arch_spinlock_t *)&lws_lock_start[index];
> arch_spin_unlock(s);
> local_irq_restore(*flags);
--
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