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blk_init_queue(9) [centos man page]

BLK_INIT_QUEUE(9)						   Block Devices						 BLK_INIT_QUEUE(9)

blk_init_queue - prepare a request queue for use with a block device SYNOPSIS
struct request_queue * blk_init_queue(request_fn_proc * rfn, spinlock_t * lock); ARGUMENTS
rfn The function to be called to process requests that have been placed on the queue. lock Request queue spin lock DESCRIPTION
If a block device wishes to use the standard request handling procedures, which sorts requests and coalesces adjacent requests, then it must call blk_init_queue. The function rfn will be called when there are requests on the queue that need to be processed. If the device supports plugging, then rfn may not be called immediately when requests are available on the queue, but may be called at some time later instead. Plugged queues are generally unplugged when a buffer belonging to one of the requests on the queue is needed, or due to memory pressure. rfn is not required, or even expected, to remove all requests off the queue, but only as many as it can handle at a time. If it does leave requests on the queue, it is responsible for arranging that the requests get dealt with eventually. The queue spin lock must be held while manipulating the requests on the request queue; this lock will be taken also from interrupt context, so irq disabling is needed for it. Function returns a pointer to the initialized request queue, or NULL if it didn't succeed. NOTE
blk_init_queue must be paired with a blk_cleanup_queue call when the block device is deactivated (such as at module unload). COPYRIGHT
Kernel Hackers Manual 3.10 June 2014 BLK_INIT_QUEUE(9)

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Perlbal::Manual::HighPriority(3pm)			User Contributed Perl Documentation			Perlbal::Manual::HighPriority(3pm)

Perlbal::Manual::HighPriority - Perlbal's high/low priority queueing system. VERSION Perlbal 1.78. DESCRIPTION This document describes Perlbal's high/low priority queueing system. Queuing system Perlbal has three queues: normal, high priority and low priority. As their names suggest, this means that usually requests get to the normal queue and are dispatched in FIFO order, with high priority requests going to a different queue that gets ahead of the normal one and a low priority queue that only gets done when the high and normal queues are empty. In a nutshell, whenever Perlbal needs to select which request to take care of next, it first looks for requests in the high priority queue; if that one is empty, it then looks into the normal queue; and, if the normal queue is empty too, it finally looks in the low priority queue. High priority with cookies Perlbal can use cookies to determine if a request should go to the high priority queue (configurable). The parameters to configure this are "high_priority_cookie" and "high_priority_cookie_contents"; the first defines the name of the field to check for on the cookie and the second one defines the content in that field that will trigger the request going to the fast queue: SET myservice.high_priority_cookie = name_of_the_field SET myservice.high_priority_cookie_contents = required_content_on_that_field Here's a clearer example: SET myservice.high_priority_cookie = highpriority SET myservice.high_priority_cookie_contents = yes High priority with plugins The plugin Perlbal::Plugin::Highpri supports making requests high priority by URI or Host. Also check "make_high_priority" under Perlbal::Manual::Hooks. Queue relief Sometimes if the high priority queue is really busy, the standard queue will suffer from resource starvation. The queue relief system helps prevent this. When there are "queue_relief_size" or more connections in the standard queue, newly available backends have a "queue_relief_chance" percent chance of taking a request from the standard priority queue instead of the high priority queue. SET web_proxy.queue_relief_size = 2000 SET web_proxy.queue_relief_chance = 30 # 0-100, in percent SEE ALSO "make_high_priority" and "make_low_priority" in Perlbal::Manual::Hooks, Perlbal::Plugin::HighPriority. perl v5.14.2 2011-01-23 Perlbal::Manual::HighPriority(3pm)
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