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# qstats.stp: Queue statistics gathering tapset
/* <tapsetdescription>
* The queue_stats tapset provides functions that,
* given notifications of elementary queuing events (wait, run, done),
* tracks averages such as queue length, service and wait times,
* utilization.
*
* The functions qs_wait(), qs_run(), and qs_done() should be called
* from appropriate probes, in sequence.
*
* Functions with the prefix qsq_ are for querying the statistics averaged
* since the first queue operation (or when qsq_start() was called).
* Since statistics are often fractional, a scale parameter is used to
* multiply the result to a more useful scale. For some fractions, a scale
* of 100 will usefully return percentage numbers.
* </tapsetdescription>
*/
# ------------------------------------------------------------------------
# The default timing function: microseconds. This function could
# go into a separate file (say, qstats_qs_time.stp), so that a user
# script can override it with another definition.
/* XXX: docstring */
function qs_time () { return gettimeofday_us () }
# ------------------------------------------------------------------------
@__private30 global qs_wtime, qs_wlentime, qs_wcount
@__private30 global qs_rtime, qs_rlentime, qs_rcount
@__private30 global qs_stime, qs_utime, qs_dcount
# ------------------------------------------------------------------------
@__private30 function _qs_update (qname) {
now = qs_time ()
then = qs_utime[qname]; if (! then) { then = now }
delta = now-then
qs_wtime[qname] += qs_wcount[qname] ? delta : 0
qs_wlentime[qname] += qs_wcount[qname] * delta
qs_rtime[qname] += qs_rcount[qname] ? delta : 0
qs_rlentime[qname] += qs_rcount[qname] * delta
qs_utime[qname] = now
}
/**
* sfunction qs_wait - Function to record enqueue requests
* @qname: the name of the queue requesting enqueue
*
* Description: This function records that a new request
* was enqueued for the given queue name.
*/
function qs_wait (qname:string) { # enqueueing request
_qs_update (qname)
qs_wcount[qname] ++
}
/**
* sfunction qs_run - Function to record being moved from wait queue to being serviced
* @qname: the name of the service being moved and started
*
* Description: This function records that the previous enqueued
* request was removed from the given wait queue and is now
* being serviced.
*/
function qs_run (qname:string) { # starting to service request
_qs_update (qname)
if (qs_wcount[qname] > 0) {
qs_wcount[qname] --
qs_rcount[qname] ++
}
}
/**
* sfunction qs_done - Function to record finishing request
* @qname: the name of the service that finished
*
* Description: This function records that a request
* originally from the given queue has completed being
* serviced.
*/
function qs_done (qname:string) { # done servicing request
_qs_update (qname)
if (qs_rcount[qname] > 0) {
qs_rcount[qname] --
qs_dcount[qname] ++
}
}
# ------------------------------------------------------------------------
/**
* sfunction qsq_start - Function to reset the stats for a queue
* @qname: the name of the service that finished
*
* Description: This function resets the statistics counters for the given
* queue, and restarts tracking from the moment the function was called.
* This function is also used to create intialize a queue.
*/
function qsq_start (qname:string) { # reset statistics for new baseline
qs_rcount[qname] = 0
delete qs_rtime[qname]
delete qs_rlentime[qname]
qs_wcount[qname] = 0
delete qs_wtime[qname]
delete qs_wlentime[qname]
delete qs_dcount[qname]
delete qs_utime[qname]
qs_stime[qname] = qs_time ()
}
# ------------------------------------------------------------------------
# Various query functions. Each returns the average, taken over the time
# interval from the last qsq_start(). Most deal with fractions, and so
# also take a scale parameter (use 100 for percent).
/**
* sfunction qsq_utilization - Fraction of time that any request was being serviced
* @qname: queue name
* @scale: scale variable to take account for interval fraction
*
* Description: This function returns the average time in microseconds
* that at least one request was being serviced.
*/
function qsq_utilization:long (qname:string, scale:long) {
_qs_update (qname)
elapsed = qs_time() - qs_stime[qname]
return (scale * qs_rtime[qname]) / elapsed
}
# fraction of time that any request was blocked in the wait queue
/**
* sfunction qsq_blocked - Returns the time reqest was on the wait queue
* @qname: queue name
* @scale: scale variable to take account for interval fraction
*
* Description: This function returns the fraction of elapsed time during
* which one or more requests were on the wait queue.
*/
function qsq_blocked:long (qname:string, scale:long) {
_qs_update (qname)
elapsed = qs_time() - qs_stime[qname]
return (scale * qs_wtime[qname]) / elapsed
}
# length of wait queue
/**
* sfunction qsq_wait_queue_length - length of wait queue
* @qname: queue name
* @scale: scale variable to take account for interval fraction
*
* Description: This function returns the average length of the wait queue
*/
function qsq_wait_queue_length:long (qname:string, scale:long) {
_qs_update (qname)
elapsed = qs_time() - qs_stime[qname]
return (scale * qs_wlentime[qname]) / elapsed
}
/**
* sfunction qsq_service_time - Amount of time per request service
* @qname: queue name
* @scale: scale variable to take account for interval fraction
*
* Description: This function returns the average time in microseconds
* required to service a request once it is removed from the wait queue.
*/
function qsq_service_time:long (qname:string, scale:long) {
_qs_update (qname)
return (scale * qs_rlentime[qname]) / qs_dcount[qname]
}
/**
* sfunction qsq_wait_time - Amount of time in queue + service per request
* @qname: queue name
* @scale: scale variable to take account for interval fraction
*
* Description: This function returns the average time in microseconds
* that it took for a request to be serviced (qs_wait() to qa_done()).
*/
function qsq_wait_time:long (qname:string, scale:long) {
_qs_update (qname)
return (scale * (qs_rlentime[qname] + qs_wlentime[qname]))
/ qs_dcount[qname]
}
/**
* sfunction qsq_throughput - Number of requests served per unit time
* @qname: queue name
* @scale: scale variable to take account for interval fraction
*
* Description: This function returns the average number or requests
* served per microsecond.
*/
function qsq_throughput:long (qname:string, scale:long) {
_qs_update (qname)
elapsed = qs_time() - qs_stime[qname]
return (scale * qs_dcount[qname]) / elapsed
}
# ------------------------------------------------------------------------
/**
* sfunction qsq_print - Prints a line of statistics for the given queue
* @qname: queue name
*
* Description: This function prints a line containing the following
* statistics for the given queue:
* the queue name,
* the average rate of requests per second,
* the average wait queue length,
* the average time on the wait queue,
* the average time to service a request,
* the percentage of time the wait queue was used,
* and the percentage of time request was being serviced.
*/
function qsq_print (qname:string) {
qt = qsq_throughput (qname, 1000000000) # 1000 * (number of requests served per second)
qwl = qsq_wait_queue_length (qname, 1000)
printf("%s: %d.%03d ops/s, %d.%03d qlen, %d await, %d svctm, %d%% wait, %d%% util\n",
qname,
qt/1000, qt%1000,
qwl/1000, qwl%1000,
qsq_wait_time (qname, 1),
qsq_service_time (qname, 1),
qsq_blocked (qname, 100),
qsq_utilization (qname, 100))
}
/* What follows in an example form src/testsuite/systemtap.samples/queue_demo.stp
* It uses the randomize feature of the timer probe to simulate queuing activity.
*
* probe begin {
* qsq_start ("block-read")
* qsq_start ("block-write")
* }
*
* probe timer.ms(3500), end {
* qsq_print ("block-read")
* qsq_start ("block-read")
* qsq_print ("block-write")
* qsq_start ("block-write")
* }
*
* probe timer.ms(10000) {
* exit()
* }
*
* // synthesize queue work/service using three randomized "threads" for each queue.
* global tc
*
* function qs_doit (thread, name) {
* n = tc[thread] = (tc[thread]+1) % 3 //per-thread state counter
* if (n==1) qs_wait (name)
* else if (n==2) qs_run (name)
* else if (n==0) qs_done (name)
* }
*
* probe timer.ms(100).randomize(100) { qs_doit (0, "block-read") }
* probe timer.ms(100).randomize(100) { qs_doit (1, "block-read") }
* probe timer.ms(100).randomize(100) { qs_doit (2, "block-read") }
* probe timer.ms(100).randomize(100) { qs_doit (3, "block-write") }
* probe timer.ms(100).randomize(100) { qs_doit (4, "block-write") }
* probe timer.ms(100).randomize(100) { qs_doit (5, "block-write") }
*
* //This prints:
* block-read: 9 ops/s, 1.090 qlen, 215749 await, 96382 svctm, 69% wait, 64% util
* block-write: 9 ops/s, 0.992 qlen, 208485 await, 103150 svctm, 69% wait, 61% util
* block-read: 9 ops/s, 0.968 qlen, 197411 await, 97762 svctm, 63% wait, 63% util
* block-write: 8 ops/s, 0.930 qlen, 202414 await, 93870 svctm, 60% wait, 56% util
* block-read: 8 ops/s, 0.744 qlen, 192957 await, 99995 svctm, 58% wait, 62% util
* block-write: 9 ops/s, 0.861 qlen, 193857 await, 101573 svctm, 56% wait, 64% util
*/