From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: RFC: Allow block drivers to poll for I/O instead of sleeping Date: Thu, 27 Jun 2013 14:42:33 -0400 Message-ID: <51CC8799.9070909@redhat.com> References: <20130620201713.GV8211@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130620201713.GV8211@linux.intel.com> Sender: linux-kernel-owner@vger.kernel.org To: Matthew Wilcox Cc: Jens Axboe , Al Viro , Ingo Molnar , linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, linux-scsi@vger.kernel.org, Linus Torvalds List-Id: linux-scsi@vger.kernel.org On 06/20/2013 04:17 PM, Matthew Wilcox wrote: > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4527,6 +4527,36 @@ long __sched io_schedule_timeout(long timeout) > return ret; > } > > +/* > + * Wait for an I/O to complete against this backing_dev_info. If the > + * task exhausts its timeslice polling for completions, call io_schedule() > + * anyway. If a signal comes pending, return so the task can handle it. > + * If the io_poll returns an error, give up and call io_schedule(), but > + * swallow the error. We may miss an I/O completion (eg if the interrupt > + * handler gets to it first). Guard against this possibility by returning > + * if we've been set back to TASK_RUNNING. > + */ > +void io_wait(struct backing_dev_info *bdi) > +{ I would like something a little more generic in the scheduler code, that could also be used by other things in the kernel (say, KVM with message passing workloads). Maybe something looking a little like this? void idle_poll(struct idle_poll_info *ipi) struct idle_poll_info { int (*idle_poll_func)(void *data); int (*idle_poll_preempt)(void *data); void *data; } That way the kernel can: 1) mark the current thread as having idle priority, allowing the scheduler to preempt it if something else wants to run 2) switch to asynchronous mode if something else wants to run, or if the average wait for the process is so long that it is better to go asynchronous and avoid polling 3) poll for completion if nothing else wants to run Does that make sense? Did I forget something you need? Did I forget something KVM could need? Is this insane? If so, is it too insane? :)