There would be a single work queue (kblockd) for all block devices on which deffered work of different block device queues will be queued after the unplug_timer.
----- Original Message ----- From: "Rajat Jain, Noida" <[EMAIL PROTECTED]> To: "lk" <[EMAIL PROTECTED]>; <linux-scsi@vger.kernel.org>; <[EMAIL PROTECTED]>; <linux-newbie@vger.kernel.org> Sent: Wednesday, March 23, 2005 12:49 AM Subject: RE: When & how is the SCSI strategy routine called? > > > Thanks lk. > > It cleared a lot of things. > > How ever, what I am wondering is: > > - Does each device queue have a corresponding thread that is woken up when > it is time to call the request function? And the request function is called > in the context of this thread? > > - I explored and found that there is some "worker thread" kblockd that does > this task of monitoring the queue and calling the request function. I want > to know whether there is a separate thread for each queue (device) , or just > one for all the block devices? > > TIA, > > Rajat > > > -----Original Message----- > From: lk [mailto:[EMAIL PROTECTED] > Sent: Wednesday, March 23, 2005 1:29 PM > To: linux-scsi@vger.kernel.org; [EMAIL PROTECTED]; > linux-newbie@vger.kernel.org > Subject: Re:When & how is the SCSI strategy routine called? > > This is my understanding. > scsi_request_fn is the scsi's request function which performs the actual > data transfer. clean up the queue and loop back to fetch next request. > > About the Question:WHEN and HOW is the strategy routine "scsi_request_fn()" > called ? > > Every request queue have a few members to decide whether to call > scsi_request_fn() or not. scsi_request_fn is called after the queue is > unplugged. > > request_queue_t->unplug_thresh > Whenever request queue is about to get full. which is the number of > requests after which the queue should be unplugged. unplugging of request > will in turn call scsi_request_fn(). > > request_queue_t->unplug_timer > After this much time the queue will be unplugged to rip the IO in turn > it will call scsi_request_fn(). > > Also in case of Async Direct IO the block layer will unplug the queue > after > submission of bios to queue by calling blk_run_address_space function. > > scsi_request_fn will be called whenever the block layer calls queue unplug > or > queue is about to get full or after a certain unplug timer value. > > Hope it helps. > > > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] Behalf Of Rajat Jain, Noida > Sent: Tuesday, March 22, 2005 8:31 AM > To: linux-scsi@vger.kernel.org; linux-newbie@vger.kernel.org > Cc: Rajat Jain, Noida > Subject: When & how is the SCSI strategy routine called? > > > Hi list, > > Tracing the kernel 2.6.8 code I found that scsi_mod maintains separate > request queues for each SCSI device. It uses the block layer queuing > facility to do this. What I could not find out was that once a request is > queued into a queue (for a particular device), WHEN and HOW is the strategy > routine "scsi_request_fn()" called ? > > All I could find on the net was that "The kernel calls the strategy routine > when ever it believes that it is appropriate to invoke it." > > Please help ... Any pointers will be highly appreciated. > > TIA, > > Rajat > > > > > Disclaimer: > > This message and any attachment(s) contained here are information that is > confidential,proprietary to HCL Technologies and its customers, privileged > or otherwise protected by law.The information is solely intended for the > individual or the entity it is addressed to. If you are not the intended > recipient of this message, you are not authorized to read, forward, > print,retain, copy or disseminate this message or any part of it. If you > have received this e-mail in error, please notify the sender immediately by > return e-mail and delete it from your computer. > > > - > To unsubscribe from this list: send the line "unsubscribe linux-scsi" in > the body of a message to [EMAIL PROTECTED] > More majordomo info at http://vger.kernel.org/majordomo-info.html - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
