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From: Tejun Heo <tj@kernel.org>
To: Daniel Jordan <daniel.m.jordan@oracle.com>
Cc: linux-mm@kvack.org, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, aarcange@redhat.com,
	aaron.lu@intel.com, akpm@linux-foundation.org,
	alex.williamson@redhat.com, bsd@redhat.com,
	darrick.wong@oracle.com, dave.hansen@linux.intel.com,
	jgg@mellanox.com, jwadams@google.com, jiangshanlai@gmail.com,
	mhocko@kernel.org, mike.kravetz@oracle.com,
	Pavel.Tatashin@microsoft.com, prasad.singamsetty@oracle.com,
	rdunlap@infradead.org, steven.sistare@oracle.com,
	tim.c.chen@intel.com, vbabka@suse.cz
Subject: Re: [RFC PATCH v4 05/13] workqueue, ktask: renice helper threads to prevent starvation
Date: Tue, 13 Nov 2018 08:34:00 -0800
Message-ID: <20181113163400.GK2509588@devbig004.ftw2.facebook.com> (raw)
In-Reply-To: <20181105165558.11698-6-daniel.m.jordan@oracle.com>

Hello, Daniel.

On Mon, Nov 05, 2018 at 11:55:50AM -0500, Daniel Jordan wrote:
>  static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
> -			     bool from_cancel)
> +			     struct nice_work *nice_work, int flags)
>  {
>  	struct worker *worker = NULL;
>  	struct worker_pool *pool;
> @@ -2868,11 +2926,19 @@ static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr,
>  	if (pwq) {
>  		if (unlikely(pwq->pool != pool))
>  			goto already_gone;
> +
> +		/* not yet started, insert linked work before work */
> +		if (unlikely(flags & WORK_FLUSH_AT_NICE))
> +			insert_nice_work(pwq, nice_work, work);

So, I'm not sure this works that well.  e.g. what if the work item is
waiting for other work items which are at lower priority?  Also, in
this case, it'd be a lot simpler to simply dequeue the work item and
execute it synchronously.

>  	} else {
>  		worker = find_worker_executing_work(pool, work);
>  		if (!worker)
>  			goto already_gone;
>  		pwq = worker->current_pwq;
> +		if (unlikely(flags & WORK_FLUSH_AT_NICE)) {
> +			set_user_nice(worker->task, nice_work->nice);
> +			worker->flags |= WORKER_NICED;
> +		}
>  	}

I'm not sure about this.  Can you see whether canceling & executing
synchronously is enough to address the latency regression?

Thanks.

-- 
tejun

  reply index

Thread overview: 54+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-05 16:55 [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 01/13] ktask: add documentation Daniel Jordan
2018-11-05 21:19   ` Randy Dunlap
2018-11-06  2:27     ` Daniel Jordan
2018-11-06  8:49   ` Peter Zijlstra
2018-11-06 20:34     ` Daniel Jordan
2018-11-06 20:51       ` Jason Gunthorpe
2018-11-07 10:27         ` Peter Zijlstra
2018-11-07 20:21           ` Daniel Jordan
2018-11-07 10:35       ` Peter Zijlstra
2018-11-07 21:20         ` Daniel Jordan
2018-11-08 17:26   ` Jonathan Corbet
2018-11-08 19:15     ` Daniel Jordan
2018-11-08 19:24       ` Jonathan Corbet
2018-11-27 19:50   ` Pavel Machek
2018-11-28 16:56     ` Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 02/13] ktask: multithread CPU-intensive kernel work Daniel Jordan
2018-11-05 20:51   ` Randy Dunlap
2018-11-06  2:24     ` Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 03/13] ktask: add undo support Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 04/13] ktask: run helper threads at MAX_NICE Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 05/13] workqueue, ktask: renice helper threads to prevent starvation Daniel Jordan
2018-11-13 16:34   ` Tejun Heo [this message]
2018-11-19 16:45     ` Daniel Jordan
2018-11-20 16:33       ` Tejun Heo
2018-11-20 17:03         ` Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 06/13] vfio: parallelize vfio_pin_map_dma Daniel Jordan
2018-11-05 21:51   ` Alex Williamson
2018-11-06  2:42     ` Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 07/13] mm: change locked_vm's type from unsigned long to atomic_long_t Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 08/13] vfio: remove unnecessary mmap_sem writer acquisition around locked_vm Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 09/13] vfio: relieve mmap_sem reader cacheline bouncing by holding it longer Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 10/13] mm: enlarge type of offset argument in mem_map_offset and mem_map_next Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 11/13] mm: parallelize deferred struct page initialization within each node Daniel Jordan
2018-11-10  3:48   ` Elliott, Robert (Persistent Memory)
2018-11-12 16:54     ` Daniel Jordan
2018-11-12 22:15       ` Elliott, Robert (Persistent Memory)
2018-11-19 16:01         ` Daniel Jordan
2018-11-27  0:12           ` Elliott, Robert (Persistent Memory)
2018-11-27 20:23             ` Daniel Jordan
2018-11-19 16:29       ` Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 12/13] mm: parallelize clear_gigantic_page Daniel Jordan
2018-11-05 16:55 ` [RFC PATCH v4 13/13] hugetlbfs: parallelize hugetlbfs_fallocate with ktask Daniel Jordan
2018-11-05 17:29 ` [RFC PATCH v4 00/13] ktask: multithread CPU-intensive kernel work Michal Hocko
2018-11-06  1:29   ` Daniel Jordan
2018-11-06  9:21     ` Michal Hocko
2018-11-07 20:17       ` Daniel Jordan
2018-11-05 18:49 ` Zi Yan
2018-11-06  2:20   ` Daniel Jordan
2018-11-06  2:48     ` Zi Yan
2018-11-06 19:00       ` Daniel Jordan
2018-11-30 19:18 ` Tejun Heo
2018-12-01  0:13   ` Daniel Jordan
2018-12-03 16:16     ` Tejun Heo

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