From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi1-x244.google.com (mail-oi1-x244.google.com [IPv6:2607:f8b0:4864:20::244]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by ml01.01.org (Postfix) with ESMTPS id 757F42112870A for ; Thu, 27 Sep 2018 19:48:54 -0700 (PDT) Received: by mail-oi1-x244.google.com with SMTP id a203-v6so4088478oib.0 for ; Thu, 27 Sep 2018 19:48:54 -0700 (PDT) MIME-Version: 1.0 References: <20180926214433.13512.30289.stgit@localhost.localdomain> <20180926215149.13512.51991.stgit@localhost.localdomain> <021d55fb-9f6a-0b52-3513-e9c5493bd7d7@linux.intel.com> In-Reply-To: <021d55fb-9f6a-0b52-3513-e9c5493bd7d7@linux.intel.com> From: Dan Williams Date: Thu, 27 Sep 2018 19:48:42 -0700 Message-ID: Subject: Re: [RFC workqueue/driver-core PATCH 3/5] driver core: Probe devices asynchronously instead of the driver List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: linux-nvdimm-bounces@lists.01.org Sender: "Linux-nvdimm" To: alexander.h.duyck@linux.intel.com Cc: "Brown, Len" , Linux-pm mailing list , Greg KH , linux-nvdimm , jiangshanlai@gmail.com, Linux Kernel Mailing List , zwisler@kernel.org, Pavel Machek , Tejun Heo , Andrew Morton , "Rafael J. Wysocki" List-ID: On Thu, Sep 27, 2018 at 8:31 AM Alexander Duyck wrote: > > > > On 9/26/2018 5:48 PM, Dan Williams wrote: > > On Wed, Sep 26, 2018 at 2:51 PM Alexander Duyck > > wrote: > >> > >> This change makes it so that we probe devices asynchronously instead of the > >> driver. This results in us seeing the same behavior if the device is > >> registered before the driver or after. This way we can avoid serializing > >> the initialization should the driver not be loaded until after the devices > >> have already been added. > >> > >> The motivation behind this is that if we have a set of devices that > >> take a significant amount of time to load we can greatly reduce the time to > >> load by processing them in parallel instead of one at a time. In addition, > >> each device can exist on a different node so placing a single thread on one > >> CPU to initialize all of the devices for a given driver can result in poor > >> performance on a system with multiple nodes. > >> > >> One issue I can see with this patch is that I am using the > >> dev_set/get_drvdata functions to store the driver in the device while I am > >> waiting on the asynchronous init to complete. For now I am protecting it by > >> using the lack of a dev->driver and the device lock. > >> > >> Signed-off-by: Alexander Duyck > > [..] > >> @@ -891,6 +914,25 @@ static int __driver_attach(struct device *dev, void *data) > >> return ret; > >> } /* ret > 0 means positive match */ > >> > >> + if (driver_allows_async_probing(drv)) { > >> + /* > >> + * Instead of probing the device synchronously we will > >> + * probe it asynchronously to allow for more parallelism. > >> + * > >> + * We only take the device lock here in order to guarantee > >> + * that the dev->driver and driver_data fields are protected > >> + */ > >> + dev_dbg(dev, "scheduling asynchronous probe\n"); > >> + device_lock(dev); > >> + if (!dev->driver) { > >> + get_device(dev); > >> + dev_set_drvdata(dev, drv); > >> + async_schedule(__driver_attach_async_helper, dev); > > > > I'm not sure async drivers / sub-systems are ready for their devices > > to show up in parallel. While userspace should not be relying on > > kernel device names, people get upset when devices change kernel names > > from one boot to the next, and I can see this change leading to that > > scenario. > > The thing is the current async behavior already does this if the driver > is loaded before the device is added. All I am doing is making the > behavior with the driver loaded first the standard instead of letting it > work the other way around. This way we get consistent behavior. Ok, I can see the consistency argument. It's still a behavior change that needs testing. Configurations that have been living with the default of synchronous probing of the devices on the bus for a later arriving driver might be surprised. That said, I was confusing async probing with device registration in my thinking, so some of the discovery order / naming concerns may not be as bad as I was imagining. Sub-systems that would be broken by this behavior change would already be broken if a driver is built-in vs module. So, consider this, an Acked-by. > > If a driver / sub-system wants more parallelism than what > > driver_allows_async_probing() provides it should do it locally, for > > example, like libata does. > > So where I actually saw this was with the pmem legacy setup I had. After > doing all the work to parallelize things in the driver it had no effect. > That was because the nd_pmem driver wasn't loaded yet so all the > device_add calls did is add the device but didn't attach the nd_pmem > driver. Then when the driver loaded it serialized the probe calls > resulting in it taking twice as long as it needed to in order to > initialize the memory. > > This seems to affect standard persistent memory as well. The only > difference is that instead of probing the device on the first pass we > kick it back and reprobe it in nd_pmem_probe/nd_pfn_probe in order to > set the correct personality and that in turn allows us to asynchronously > reschedule the work on the correct CPU and deserialize it. I don't see any problems with this series with the nvdimm unit tests, but note those tests do not check for discovery order / naming discrepancies. _______________________________________________ Linux-nvdimm mailing list Linux-nvdimm@lists.01.org https://lists.01.org/mailman/listinfo/linux-nvdimm