[Virtio-fs] [External] [RFC] [PATCH] virtiofsd: Auto switch between inline and thread-pool processing

[Jiachen Zhang]

On Sat, Apr 24, 2021 at 5:11 AM Vivek Goyal <vgoyal at redhat.com> wrote:

> This is just an RFC patch for now. I am still running performance numbers
> and see if this method of switching is good enough or not. I did one run
> and seemed to get higher performance on deeper queue depths. There were
> few tests where I did not match lower queue depth performance with
> no thread pool. May be run to run variation.
>
>
I think this is interesting. I guess the switch number between thread-pool
and the inline method may change as the hardware or OS kernel changes.
Looking forward to the results.

Jiachen


> For low queue depth workloads, inline processing works well. But for
> high queue depth (and multiple process/thread) workloads, parallel
> processing of thread pool can benefit.
>
> This patch is an experiment which tries to switch to between inline and
> thread-pool processing. If number of requests received on queue is
> 1, inline processing is done. Otherwise requests are handed over to
> a thread pool for processing.
>
> Signed-off-by: Vivek Goyal <vgoyal at redhat.com>
> ---
>  tools/virtiofsd/fuse_virtio.c |   27 +++++++++++++++++++--------
>  1 file changed, 19 insertions(+), 8 deletions(-)
>
> Index: rhvgoyal-qemu/tools/virtiofsd/fuse_virtio.c
> ===================================================================
> --- rhvgoyal-qemu.orig/tools/virtiofsd/fuse_virtio.c    2021-04-23
> 10:03:46.175920039 -0400
> +++ rhvgoyal-qemu/tools/virtiofsd/fuse_virtio.c 2021-04-23
> 10:56:37.793722634 -0400
> @@ -446,6 +446,15 @@ err:
>  static __thread bool clone_fs_called;
>
>  /* Process one FVRequest in a thread pool */
> +static void fv_queue_push_to_pool(gpointer data, gpointer user_data)
> +{
> +    FVRequest *req = data;
> +    GThreadPool *pool = user_data;
> +
> +    g_thread_pool_push(pool, req, NULL);
> +}
> +
> +/* Process one FVRequest in a thread pool */
>  static void fv_queue_worker(gpointer data, gpointer user_data)
>  {
>      struct fv_QueueInfo *qi = user_data;
> @@ -605,6 +614,7 @@ static void *fv_queue_thread(void *opaqu
>      struct fuse_session *se = qi->virtio_dev->se;
>      GThreadPool *pool = NULL;
>      GList *req_list = NULL;
> +    int nr_req = 0;
>
>      if (se->thread_pool_size) {
>          fuse_log(FUSE_LOG_DEBUG, "%s: Creating thread pool for Queue
> %d\n",
> @@ -686,22 +696,23 @@ static void *fv_queue_thread(void *opaqu
>              }
>
>              req->reply_sent = false;
> -
> -            if (!se->thread_pool_size) {
> -                req_list = g_list_prepend(req_list, req);
> -            } else {
> -                g_thread_pool_push(pool, req, NULL);
> -            }
> +            req_list = g_list_prepend(req_list, req);
> +            nr_req++;
>          }
>
>          pthread_mutex_unlock(&qi->vq_lock);
>          vu_dispatch_unlock(qi->virtio_dev);
>
>          /* Process all the requests. */
> -        if (!se->thread_pool_size && req_list != NULL) {
> -            g_list_foreach(req_list, fv_queue_worker, qi);
> +        if (req_list != NULL) {
> +            if (!se->thread_pool_size || nr_req <= 2) {
> +                g_list_foreach(req_list, fv_queue_worker, qi);
> +            } else  {
> +                g_list_foreach(req_list, fv_queue_push_to_pool, pool);
> +            }
>              g_list_free(req_list);
>              req_list = NULL;
> +            nr_req = 0;
>          }
>      }
>
>
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