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
