Re: [Qemu-devel] [RFC PATCH 3/3] qemu-coroutine: use a ring per thread for the pool

[Paolo Bonzini <pbonzini@redhat.com>]

On 28/11/2014 12:32, Peter Lieven wrote:
> Am 28.11.2014 um 12:23 schrieb Paolo Bonzini:
>>
>> On 28/11/2014 12:21, Peter Lieven wrote:
>>> Am 28.11.2014 um 12:14 schrieb Paolo Bonzini:
>>>>> master:
>>>>> Run operation 40000000 iterations 12.851414 s, 3112K operations/s, 321ns per coroutine
>>>>>
>>>>> paolo:
>>>>> Run operation 40000000 iterations 11.951720 s, 3346K operations/s, 298ns per coroutine
>>>> Nice. :)
>>>>
>>>> Can you please try "coroutine: Use __thread … " together, too?  I still
>>>> see 11% time spent in pthread_getspecific, and I get ~10% more indeed if
>>>> I apply it here (my times are 191/160/145).
>>> indeed:
>>>
>>> Run operation 40000000 iterations 10.138684 s, 3945K operations/s, 253ns per coroutine
>> Your perf_master2 uses the ring buffer unconditionally, right?  I wonder
>> if we can use a similar algorithm but with arrays instead of lists...
> 
> Why do you set pool_size = 0 in the create path?
> 
> When I do the following:
> diff --git a/qemu-coroutine.c b/qemu-coroutine.c
> index 6bee354..c79ee78 100644
> --- a/qemu-coroutine.c
> +++ b/qemu-coroutine.c
> @@ -44,7 +44,7 @@ Coroutine *qemu_coroutine_create(CoroutineEntry *entry)
>                   * and the actual size of alloc_pool.  But it is just a heuristic,
>                   * it does not need to be perfect.
>                   */
> -                pool_size = 0;
> +                atomic_dec(&pool_size);
>                  QSLIST_MOVE_ATOMIC(&alloc_pool, &release_pool);
>                  co = QSLIST_FIRST(&alloc_pool);
> 
> 
> I get:
> Run operation 40000000 iterations 9.883958 s, 4046K operations/s, 247ns per coroutine

Because pool_size is the (approximate) number of coroutines in the pool.
 It is zero after QSLIST_MOVE_ATOMIC has NULL-ed out release_pool.slh_first.

Paolo