From mboxrd@z Thu Jan 1 00:00:00 1970 From: ming.lei@redhat.com (Ming Lei) Date: Wed, 17 Jan 2018 18:17:32 +0800 Subject: [PATCH 2/2] blk-mq: simplify queue mapping & schedule with each possisble CPU In-Reply-To: References: <20180116121010.GA26429@ming.t460p> <7c24e321-2d3b-cdec-699a-f58c34300aa9@oracle.com> <20180116153248.GA3018@ming.t460p> <7f5bad86-febc-06fc-67c0-393777d172e4@oracle.com> <20180117035159.GA9487@ming.t460p> <8c8efce8-ea02-0a9e-8369-44c885f4731d@oracle.com> <20180117062251.GC9487@ming.t460p> <977e9c62-c7f2-d1df-7d6b-5903f3b21cb6@oracle.com> <20180117095744.GF9487@ming.t460p> Message-ID: <20180117101731.GG9487@ming.t460p> On Wed, Jan 17, 2018@11:07:48AM +0100, Christian Borntraeger wrote: > > > On 01/17/2018 10:57 AM, Ming Lei wrote: > > Hi Jianchao, > > > > On Wed, Jan 17, 2018@04:09:11PM +0800, jianchao.wang wrote: > >> Hi ming > >> > >> Thanks for your kindly response. > >> > >> On 01/17/2018 02:22 PM, Ming Lei wrote: > >>> This warning can't be removed completely, for example, the CPU figured > >>> in blk_mq_hctx_next_cpu(hctx) can be put on again just after the > >>> following call returns and before __blk_mq_run_hw_queue() is scheduled > >>> to run. > >>> > >>> kblockd_mod_delayed_work_on(blk_mq_hctx_next_cpu(hctx), &hctx->run_work, msecs_to_jiffies(msecs)) > >> We could use cpu_active in __blk_mq_run_hw_queue() to narrow the window. > >> There is a big gap between cpu_online and cpu_active. rebind_workers is also between them. > > > > This warning is harmless, also you can't reproduce it without help of your > > special patch, I guess, :-) So the window shouldn't be a big deal. > > FWIW, every WARN_ON is problematic since there are people running with panic_on_warn. > If a condition can happen we should not use WARN_ON but something else. Agree, printk() should be fine, IMO. -- Ming