Chapter 8. IO Scheduler and block IO Tapset

probe::ioscheduler.elv_next_request — Fires when a request is retrieved from the request queue
probe::ioscheduler.elv_next_request.return — Fires when a request retrieval issues a return signal
probe::ioscheduler.elv_completed_request — Fires when a request is completed
probe::ioscheduler.elv_add_request.kp — kprobe based probe to indicate that a request was added to the request queue
probe::ioscheduler.elv_add_request.tp — tracepoint based probe to indicate a request is added to the request queue.
probe::ioscheduler.elv_add_request — probe to indicate request is added to the request queue.
probe::ioscheduler_trace.elv_completed_request — Fires when a request is
probe::ioscheduler_trace.elv_issue_request — Fires when a request is
probe::ioscheduler_trace.elv_requeue_request — Fires when a request is
probe::ioscheduler_trace.elv_abort_request — Fires when a request is aborted.
probe::ioscheduler_trace.plug — Fires when a request queue is plugged;
probe::ioscheduler_trace.unplug_io — Fires when a request queue is unplugged;
probe::ioscheduler_trace.unplug_timer — Fires when unplug timer associated
probe::ioblock.request — Fires whenever making a generic block I/O request.
probe::ioblock.end — Fires whenever a block I/O transfer is complete.
probe::ioblock_trace.bounce — Fires whenever a buffer bounce is needed for at least one page of a block IO request.
probe::ioblock_trace.request — Fires just as a generic block I/O request is created for a bio.
probe::ioblock_trace.end — Fires whenever a block I/O transfer is complete.

This family of probe points is used to probe block IO layer and IO scheduler activities. It contains the following probe points:

Name

probe::ioscheduler.elv_next_request — Fires when a request is retrieved from the request queue

Synopsis

ioscheduler.elv_next_request

Values

name: Name of the probe point
elevator_name: The type of I/O elevator currently enabled

Name

probe::ioscheduler.elv_next_request.return — Fires when a request retrieval issues a return signal

Synopsis

ioscheduler.elv_next_request.return

Values

disk_major: Disk major number of the request
rq: Address of the request
name: Name of the probe point
disk_minor: Disk minor number of the request
rq_flags: Request flags

Name

probe::ioscheduler.elv_completed_request — Fires when a request is completed

Synopsis

ioscheduler.elv_completed_request

Values

disk_major: Disk major number of the request
rq: Address of the request
name: Name of the probe point
elevator_name: The type of I/O elevator currently enabled
disk_minor: Disk minor number of the request
rq_flags: Request flags

Name

probe::ioscheduler.elv_add_request.kp — kprobe based probe to indicate that a request was added to the request queue

Synopsis

ioscheduler.elv_add_request.kp

Values

disk_major: Disk major number of the request
rq: Address of the request
q: pointer to request queue
name: Name of the probe point
elevator_name: The type of I/O elevator currently enabled
disk_minor: Disk minor number of the request
rq_flags: Request flags

Name

probe::ioscheduler.elv_add_request.tp — tracepoint based probe to indicate a request is added to the request queue.

Synopsis

ioscheduler.elv_add_request.tp

Values

disk_major: Disk major no of request.
rq: Address of request.
q: Pointer to request queue.
name: Name of the probe point
elevator_name: The type of I/O elevator currently enabled.
disk_minor: Disk minor number of request.
rq_flags: Request flags.

Name

probe::ioscheduler.elv_add_request — probe to indicate request is added to the request queue.

Synopsis

ioscheduler.elv_add_request

Values

disk_major: Disk major no of request.
rq: Address of request.
q: Pointer to request queue.
elevator_name: The type of I/O elevator currently enabled.
disk_minor: Disk minor number of request.
rq_flags: Request flags.

Name

probe::ioscheduler_trace.elv_completed_request — Fires when a request is

Synopsis

ioscheduler_trace.elv_completed_request

Values

disk_major: Disk major no of request.
rq: Address of request.
name: Name of the probe point
elevator_name: The type of I/O elevator currently enabled.
disk_minor: Disk minor number of request.
rq_flags: Request flags.

Description

completed.

Name

probe::ioscheduler_trace.elv_issue_request — Fires when a request is

Synopsis

ioscheduler_trace.elv_issue_request

Values

disk_major: Disk major no of request.
rq: Address of request.
name: Name of the probe point
elevator_name: The type of I/O elevator currently enabled.
disk_minor: Disk minor number of request.
rq_flags: Request flags.

Description

scheduled.

Name

probe::ioscheduler_trace.elv_requeue_request — Fires when a request is

Synopsis

ioscheduler_trace.elv_requeue_request

Values

disk_major: Disk major no of request.
rq: Address of request.
name: Name of the probe point
elevator_name: The type of I/O elevator currently enabled.
disk_minor: Disk minor number of request.
rq_flags: Request flags.

Description

put back on the queue, when the hadware cannot accept more requests.

Name

probe::ioscheduler_trace.elv_abort_request — Fires when a request is aborted.

Synopsis

ioscheduler_trace.elv_abort_request

Values

disk_major: Disk major no of request.
rq: Address of request.
name: Name of the probe point
elevator_name: The type of I/O elevator currently enabled.
disk_minor: Disk minor number of request.
rq_flags: Request flags.

Name

probe::ioscheduler_trace.plug — Fires when a request queue is plugged;

Synopsis

ioscheduler_trace.plug

Values

name: Name of the probe point
rq_queue: request queue

Description

ie, requests in the queue cannot be serviced by block driver.

Name

probe::ioscheduler_trace.unplug_io — Fires when a request queue is unplugged;

Synopsis

ioscheduler_trace.unplug_io

Values

name: Name of the probe point
rq_queue: request queue

Description

Either, when number of pending requests in the queue exceeds threshold or, upon expiration of timer that was activated when queue was plugged.

Name

probe::ioscheduler_trace.unplug_timer — Fires when unplug timer associated

Synopsis

ioscheduler_trace.unplug_timer

Values

name: Name of the probe point
rq_queue: request queue

Description

with a request queue expires.

Name

probe::ioblock.request — Fires whenever making a generic block I/O request.

Synopsis

ioblock.request

Values

None

Description

name - name of the probe point devname - block device name ino - i-node number of the mapped file sector - beginning sector for the entire bio flags - see below BIO_UPTODATE 0 ok after I/O completion BIO_RW_BLOCK 1 RW_AHEAD set, and read/write would block BIO_EOF 2 out-out-bounds error BIO_SEG_VALID 3 nr_hw_seg valid BIO_CLONED 4 doesn't own data BIO_BOUNCED 5 bio is a bounce bio BIO_USER_MAPPED 6 contains user pages BIO_EOPNOTSUPP 7 not supported

rw - binary trace for read/write request vcnt - bio vector count which represents number of array element (page, offset, length) which make up this I/O request idx - offset into the bio vector array phys_segments - number of segments in this bio after physical address coalescing is performed hw_segments - number of segments after physical and DMA remapping hardware coalescing is performed size - total size in bytes bdev - target block device bdev_contains - points to the device object which contains the partition (when bio structure represents a partition) p_start_sect - points to the start sector of the partition structure of the device

Context

The process makes block I/O request

Name

probe::ioblock.end — Fires whenever a block I/O transfer is complete.

Synopsis

ioblock.end

Values

None

Description

name - name of the probe point devname - block device name ino - i-node number of the mapped file bytes_done - number of bytes transferred sector - beginning sector for the entire bio flags - see below BIO_UPTODATE 0 ok after I/O completion BIO_RW_BLOCK 1 RW_AHEAD set, and read/write would block BIO_EOF 2 out-out-bounds error BIO_SEG_VALID 3 nr_hw_seg valid BIO_CLONED 4 doesn't own data BIO_BOUNCED 5 bio is a bounce bio BIO_USER_MAPPED 6 contains user pages BIO_EOPNOTSUPP 7 not supported error - 0 on success rw - binary trace for read/write request vcnt - bio vector count which represents number of array element (page, offset, length) which makes up this I/O request idx - offset into the bio vector array phys_segments - number of segments in this bio after physical address coalescing is performed. hw_segments - number of segments after physical and DMA remapping hardware coalescing is performed size - total size in bytes

Context

The process signals the transfer is done.

Name

probe::ioblock_trace.bounce — Fires whenever a buffer bounce is needed for at least one page of a block IO request.

Synopsis

ioblock_trace.bounce

Values

None

Description

name - name of the probe point q - request queue on which this bio was queued. devname - device for which a buffer bounce was needed. ino - i-node number of the mapped file bytes_done - number of bytes transferred sector - beginning sector for the entire bio flags - see below BIO_UPTODATE 0 ok after I/O completion BIO_RW_BLOCK 1 RW_AHEAD set, and read/write would block BIO_EOF 2 out-out-bounds error BIO_SEG_VALID 3 nr_hw_seg valid BIO_CLONED 4 doesn't own data BIO_BOUNCED 5 bio is a bounce bio BIO_USER_MAPPED 6 contains user pages BIO_EOPNOTSUPP 7 not supported rw - binary trace for read/write request vcnt - bio vector count which represents number of array element (page, offset, length) which makes up this I/O request idx - offset into the bio vector array phys_segments - number of segments in this bio after physical address coalescing is performed. size - total size in bytes bdev - target block device bdev_contains - points to the device object which contains the partition (when bio structure represents a partition) p_start_sect - points to the start sector of the partition structure of the device

Context

The process creating a block IO request.

Name

probe::ioblock_trace.request — Fires just as a generic block I/O request is created for a bio.

Synopsis

ioblock_trace.request

Values

None

Description

name - name of the probe point q - request queue on which this bio was queued. devname - block device name ino - i-node number of the mapped file bytes_done - number of bytes transferred sector - beginning sector for the entire bio flags - see below BIO_UPTODATE 0 ok after I/O completion BIO_RW_BLOCK 1 RW_AHEAD set, and read/write would block BIO_EOF 2 out-out-bounds error BIO_SEG_VALID 3 nr_hw_seg valid BIO_CLONED 4 doesn't own data BIO_BOUNCED 5 bio is a bounce bio BIO_USER_MAPPED 6 contains user pages BIO_EOPNOTSUPP 7 not supported

rw - binary trace for read/write request vcnt - bio vector count which represents number of array element (page, offset, length) which make up this I/O request idx - offset into the bio vector array phys_segments - number of segments in this bio after physical address coalescing is performed. size - total size in bytes bdev - target block device bdev_contains - points to the device object which contains the partition (when bio structure represents a partition) p_start_sect - points to the start sector of the partition structure of the device

Context

The process makes block I/O request

Name

probe::ioblock_trace.end — Fires whenever a block I/O transfer is complete.

Synopsis

ioblock_trace.end

Values

None

Description

rw - binary trace for read/write request vcnt - bio vector count which represents number of array element (page, offset, length) which makes up this I/O request idx - offset into the bio vector array phys_segments - number of segments in this bio after physical address coalescing is performed. size - total size in bytes bdev - target block device bdev_contains - points to the device object which contains the partition (when bio structure represents a partition) p_start_sect - points to the start sector of the partition structure of the device

Context

The process signals the transfer is done.