linux-kernel - Re: dlm: Use cmwq for send and receive workqueues

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Message-ID: <20101112161220.GA11037@redhat.com>
Date:	Fri, 12 Nov 2010 11:12:20 -0500
From:	David Teigland <teigland@...hat.com>
To:	Steven Whitehouse <swhiteho@...hat.com>
Cc:	cluster-devel@...hat.com, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: Re: dlm: Use cmwq for send and receive workqueues

On Fri, Nov 12, 2010 at 12:12:29PM +0000, Steven Whitehouse wrote:
> 
> So far as I can tell, there is no reason to use a single-threaded
> send workqueue for dlm, since it may need to send to several sockets
> concurrently. Both workqueues are set to WQ_MEM_RECLAIM to avoid
> any possible deadlocks, WQ_HIGHPRI since locking traffic is highly
> latency sensitive (and to avoid a priority inversion wrt GFS2's
> glock_workqueue) and WQ_FREEZABLE just in case someone needs to do
> that (even though with current cluster infrastructure, it doesn't
> make sense as the node will most likely land up ejected from the
> cluster) in the future.

Thanks, I'll want to do some testing with this, but my test machines do
not seem to create more than one dlm_recv workqueue thread (prior to this
patch).  Have you tested in any cases where many threads end up being
created?  I've noticed while debugging some many-cpu machines a huge
number of dlm_recv threads, which is just excessive.  Does this patch
address that?


> Signed-off-by: Steven Whitehouse <swhiteho@...hat.com>
> Cc: Tejun Heo <tj@...nel.org>
> 
> diff --git a/fs/dlm/lowcomms.c b/fs/dlm/lowcomms.c
> index 37a34c2..0893b30 100644
> --- a/fs/dlm/lowcomms.c
> +++ b/fs/dlm/lowcomms.c
> @@ -1431,14 +1431,16 @@ static void work_stop(void)
>  static int work_start(void)
>  {
>  	int error;
> -	recv_workqueue = create_workqueue("dlm_recv");
> +	recv_workqueue = alloc_workqueue("dlm_recv", WQ_MEM_RECLAIM |
> +					 WQ_HIGHPRI | WQ_FREEZEABLE, 0);
>  	error = IS_ERR(recv_workqueue);
>  	if (error) {
>  		log_print("can't start dlm_recv %d", error);
>  		return error;
>  	}
>  
> -	send_workqueue = create_singlethread_workqueue("dlm_send");
> +	send_workqueue = alloc_workqueue("dlm_send", WQ_MEM_RECLAIM |
> +					 WQ_HIGHPRI | WQ_FREEZEABLE, 0);
>  	error = IS_ERR(send_workqueue);
>  	if (error) {
>  		log_print("can't start dlm_send %d", error);
> 
> 
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