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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] How to Stop scheduler
The purpose of schedule_lock in schedule_data is to prevent race conditions when accessing schedule_data. A prerequisite for being able to do any work in Xen is knowing: * What a race condition is * How spinlocks work* How to use spinlocks (and other synchronization techniques) to avoid data races * How to avoid introducing deadlock conditions when using spinlocksYour question makes it seem like you're not familiar with the above concepts. I suggest you spend some time learning about them first, and then come back to your work with Xen. It's especially important that you have worked through several examples to develop an "instinct" for what kinds of things might be data races and what might cause deadlock. Data races and deadlock are both incredibly difficult to debug, and the scheduler is particularly prone to both. -George Pankaj Parakh wrote: Any answers plzz?? Also is what schedule_lock in schedlue_data is for ?? I tried to use it thinking it'll stop further scheduling, but it hangs my machine and the function doesnot proceed after that.. is something else I have to do to pause scheduling in XEN.On Tue, Nov 10, 2009 at 12:18 PM, Pankaj Parakh <me.pankajparakh@xxxxxxxxx> wrote:How to disable softirq in Xen, if I want that no function should be able to raise SCHEDULE_SOFTIRQ, how can I do that?? > On Thu, Nov 5, 2009 at 3:25 PM, George Dunlap > <George.Dunlap@xxxxxxxxxxxxx> wrote: >> I assume you mean, once you've paused current(), how do you get intothe scheduler to actually get it off the cpu? In Linux, you can call schedule() because each process has its own kernel stack allocated to it; the stack "remembers" where each process was in the kernel, so you can return from schedule() at the same place in the kernel once you're scheduled again. Xen only has one stack per cpu, so it cannot keep track of where *in the hypervisor* a vcpu is that gets scheduled out. Therefore, you can't call schedule() directly, as it would throw away the stack. You must raise SCHEDULE_SOFTIRQ on the current cpu, and then return back to the guest. On the way out, the softirq will call schedule() and switch to another vcpu if necessary. (It will only schedule the idle process if there are no runnable vcpus.) grep for SCHEDULE_SOFTIRQ to see examples of how this is used in Xen. -George On Thu, Nov 5, 2009 at 12:43 AM, Pankaj Parakh <me.pankajparakh@xxxxxxxxx> wrote:How can I schedule idle vcpu voluntarily without using schedule() ?? Is there any function for it already defined, or do I have to follow some steps.. ?? On Wed, Nov 4, 2009 at 5:09 PM, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:On Wed, Nov 4, 2009 at 5:59 AM, Pankaj Parakh <me.pankajparakh@xxxxxxxxx> wrote:If I take domain_update_lock for a domain, what will happen to its interrupts for IO completions or any other type..?? And will it be scheduled if I hold that lock..??Have you looked at the interrupt delivery / IO completion path, or the scheduler path, to see if those are affected by the domain_update_lock()? Xen is a bit of a twisted web; sometimes you just have to follow a web of logic around to find out what you're looking for; then, once you've come to a conclusion, test it by writing some code. For the scheduling question, you might start with looking at vcpu_runnable(). Peace, -GeorgeOn Wed, Nov 4, 2009 at 11:08 AM, Pankaj Parakh <me.pankajparakh@xxxxxxxxx> wrote:So is that means there will be no interrupt loss, and also clock in the paused domain will be in right and expected time.. ?? On Wed, Nov 4, 2009 at 12:41 AM, George Dunlap <george.dunlap@xxxxxxxxxxxxx> wrote:If you call vcpu_pause(), it atomically increments a counter in the vcpu struct. While that counter is non-zero, the vcpu *will not* be scheduled, interrupts or no. Interrupts will be delivered when it's scheduled again. -George Pankaj Parakh wrote:If I pause a vcpu/domain using those functions, say if a domain's I/O request over then its interrupt will raise and it can restart its scheduling rite..?? How this interrupts are/ can be queued so that when the vcpu is in pause state, it should nat change its state and when it come back to wait state, those interrupt will not be lost.. On Tue, Nov 3, 2009 at 5:18 PM, George Dunlap <George.Dunlap@xxxxxxxxxxxxx> wrote:Do you mean that you want to stop one specific vcpu / domain from being scheduled? If so, you're looking for the following functions: vcpu_pause(), vcpu_unpause() domain_pause(), domain_unpause(). They're defined in xen/common/domain.c. -George On Mon, Nov 2, 2009 at 9:02 PM, Pankaj Parakh <me.pankajparakh@xxxxxxxxx> wrote:Hi All, I am working on a project wherein I wanted to stop the scheduling activity in hypervisor through 'generic' part of scheduler, I have lil confusion as to what all things I need to mask/stop for disabling hypervisor to schedule any vcpu untill I want. Issues which I can think are about I/O waits or Zombie VCPUs. But how to tackle them... I dont know.. I wanted to know what all responsibility the generic scheduler holds in hypervisor, Any type of info or pointer can be useful. Thanks Pankaj Parakh _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel-- Pankaj Parakh-- Pankaj Parakh _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel-- Pankaj Parakh _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel-- Pankaj Parakh-- Pankaj Parakh-- Pankaj Parakh _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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