Re: [PATCH] virtiofsd: Use --thread-pool-size=0 to mean no thread pool

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Vivek Goyal (vgoyal@redhat.com) wrote:
> Right now we create a thread pool and main thread hands over the request
> to thread in thread pool to process. Number of threads in thread pool
> can be managed by option --thread-pool-size.
> 
> There is a chance that in case of some workloads, we might get better
> performance if we don't handover the request to a different thread
> and process in the context of thread receiving the request.
> 
> To implement that, redefine the meaning of --thread-pool-size=0 to
> mean that don't use a thread pool. Instead process the request in
> the context of thread receiving request from the queue.
> 
> I can't think how --thread-pool-size=0 is useful and hence using
> that. If it is already useful somehow, I could look at defining
> a new option say "--no-thread-pool".
> 
> I think this patch will be used more as a debug help to do comparison
> when it is more effecient to do not hand over the requests to a
> thread pool.
> 
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

I think this is OK, but you need to fix the style to match qemu rather
than kernel style.
(See qemu's scripts/checpatch.pl)

Dave

> ---
>  tools/virtiofsd/fuse_virtio.c | 33 ++++++++++++++++++++++++---------
>  1 file changed, 24 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/virtiofsd/fuse_virtio.c b/tools/virtiofsd/fuse_virtio.c
> index ff86f6d1ce..60aa7cd3e5 100644
> --- a/tools/virtiofsd/fuse_virtio.c
> +++ b/tools/virtiofsd/fuse_virtio.c
> @@ -695,13 +695,17 @@ static void *fv_queue_thread(void *opaque)
>      struct VuDev *dev = &qi->virtio_dev->dev;
>      struct VuVirtq *q = vu_get_queue(dev, qi->qidx);
>      struct fuse_session *se = qi->virtio_dev->se;
> -    GThreadPool *pool;
> -
> -    pool = g_thread_pool_new(fv_queue_worker, qi, se->thread_pool_size, FALSE,
> -                             NULL);
> -    if (!pool) {
> -        fuse_log(FUSE_LOG_ERR, "%s: g_thread_pool_new failed\n", __func__);
> -        return NULL;
> +    GThreadPool *pool = NULL;
> +    GList *req_list = NULL;
> +
> +    if (se->thread_pool_size) {
> +        fuse_log(FUSE_LOG_DEBUG, "%s: Creating thread pool for Queue %d\n", __func__, qi->qidx);
> +        pool = g_thread_pool_new(fv_queue_worker, qi, se->thread_pool_size,
> +                                 FALSE, NULL);
> +        if (!pool) {
> +            fuse_log(FUSE_LOG_ERR, "%s: g_thread_pool_new failed\n", __func__);
> +            return NULL;
> +        }
>      }
>  
>      fuse_log(FUSE_LOG_INFO, "%s: Start for queue %d kick_fd %d\n", __func__,
> @@ -780,14 +784,25 @@ static void *fv_queue_thread(void *opaque)
>              req->bad_in_num = bad_in_num;
>              req->bad_out_num = bad_out_num;
>  
> -            g_thread_pool_push(pool, req, NULL);
> +            if (!se->thread_pool_size)
> +                req_list = g_list_prepend(req_list, req);
> +            else
> +                g_thread_pool_push(pool, req, NULL);
>          }
>  
>          pthread_mutex_unlock(&qi->vq_lock);
>          pthread_rwlock_unlock(&qi->virtio_dev->vu_dispatch_rwlock);
> +
> +        // Process all the requests.
> +        if (!se->thread_pool_size && req_list != NULL) {
> +	    g_list_foreach(req_list, fv_queue_worker, qi);
> +	    g_list_free(req_list);
> +            req_list = NULL;
> +	}
>      }
>  
> -    g_thread_pool_free(pool, FALSE, TRUE);
> +    if (pool)
> +        g_thread_pool_free(pool, FALSE, TRUE);
>  
>      return NULL;
>  }
> -- 
> 2.25.4
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK