Hi!
On 27/01/2021 23:34, Peter Zijlstra wrote:
> On Wed, Jan 27, 2021 at 09:36:24PM +0100, Alexander A Sverdlin wrote:
>> From: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxx>
>>
>> Flushing the write buffer brings aroung 10% performace on the tight
>> uncontended spinlock loops on Octeon. Refer to commit 500c2e1fdbcc
>> ("MIPS: Optimize spinlocks.").
> No objection to the patch, but I don't find the above referenced commit
> to be enlightening wrt nudge_writes(). The best it has to offer is the
> comment that's already in the code.
My point was that original MIPS spinlocks had this write-buffer-flush and
it got lost on the conversion to qspinlocks. The referenced commit just
allows to see the last MIPS-specific implementation before deletion.
>> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@xxxxxxxxx>
>> ---
>> arch/mips/include/asm/spinlock.h | 3 +++
>> 1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/mips/include/asm/spinlock.h b/arch/mips/include/asm/spinlock.h
>> index 8a88eb2..0a707f3 100644
>> --- a/arch/mips/include/asm/spinlock.h
>> +++ b/arch/mips/include/asm/spinlock.h
>> @@ -24,6 +24,9 @@ static inline void queued_spin_unlock(struct qspinlock *lock)
>> /* This could be optimised with ARCH_HAS_MMIOWB */
>> mmiowb();
>> smp_store_release(&lock->locked, 0);
>> +#ifdef CONFIG_CPU_CAVIUM_OCTEON
>> + nudge_writes();
>> +#endif
>> }
>>
>> #include <asm/qspinlock.h>
--
Best regards,
Alexander Sverdlin.
