- blktrace.git
- man blkparse
The blkparse utility will attempt to combine streams of events for various devices on various CPUs, and produce a formatted output of the event information. Specifically, it will take the (machine-readable) output of the blktrace utility and convert it to a nicely formatted and human-readable form.
As with blktrace, some details concerning blkparse will help in understanding the command line options presented below.
- By default, blkparse expects to run in a post-processing mode;
one where the trace events have been saved by a previous run of
blktrace, and blkparse is combining event streams and dumping
formatted data.
blkparse may be run in a live manner concurrently with blktrace
by specifying '-i -' to blkparse, and combining it with the live
option for blktrace. An example would be:
% blktrace -d /dev/sda -o - | blkparse -i -
- You can set how many blkparse batches event reads via the '-b'
option, the default is to handle events in batches of 512.
- If you have saved event traces in blktrace with different output
names (via the -o option to blktrace), you must specify the same
input name via the '-i' option.
- The format of the output data can be controlled via the '-f' or '-F'
options.
By default, blkparse sends formatted data to standard output. This
may be changed via the '-o' option, or text output can be disabled
via the '-O' option. A merged binary stream can be produced using
the '-d' option.
RWBS DESCRIPTION
This is a small string containing at least one character ('R' for read, 'W' for write, or 'D' for block discard operation), and optionally either a 'B' (for barrier operations) or 'S' (for synchronous operations).
DEFAULT OUTPUT
The standard header (or initial fields displayed) include:
"%D %2c %8s %5T.%9t %5p %2a %3d"
Breaking this down:
%D Displays the event's device major/minor as: %3d,%-3d.
%2c CPU ID (2-character field).
%8s Sequence number
%5T.%9t
5-character field for the seconds portion of the time stamp
and a 9-character field for the nanoseconds in the time stamp.
%5p 5-character field for the process ID.
%2a 2-character field for one of the actions.
%3d 3-character field for the RWBS data.
Seeing this in action:
8,0 3 1 0.000000000 697 G W 223490 + 8 [kjournald]
The header is the data in this line up to the 223490 (starting block). The default output for all event types includes this header.
DEFAULT OUTPUT PER ACTION
C -- complete
If a payload is present, this is presented between parenthesis
following the header, followed by the error value.
If no payload is present, the sector and number of blocks are
presented (with an intervening plus (+) character).
If the -t option was specified, then the elapsed time is presented.
In either case, it is followed by the error value for the completion.
B -- bounced
D -- issued
I -- inserted
Q -- queued
If a payload is present, the number of payload bytes is output,
followed by the payload in hexadecimal between parenthesis.
If no payload is present, the sector and number of blocks are
presented (with an intervening plus (+) character).
If the -t option was specified, then the elapsed time is presented
(in parenthesis).
In either case, it is followed by the command associated with the
event (surrounded by square brackets).
F -- front merge
G -- get request
M -- back merge
S -- sleep
The starting sector and number of blocks is output (with an
intervening plus (+) character), followed by the command a
ssociated with the event (surrounded by square brackets).
P -- plug
The command associated with the event (surrounded by square
brackets) is output.
U -- unplug
T -- unplug due to timer
The command associated with the event (surrounded by square
brackets) is output, followed by the number of requests outstanding.
X -- split
The original starting sector followed by the new sector (separated
by a slash (/) is output, followed by the command associated with
the event (surrounded by square brackets).
A -- remap
Sector and length is output, along with the original device and
sector offset.
TRACE ACTIONS
The following trace actions are recognised:
C -- complete
A previously issued request has been completed.
The output will detail the sector and size of that request,
as well as the success or failure of it.
D -- issued
A request that previously resided on the block layer queue or
in the i/o scheduler has been sent to the driver.
I -- inserted
A request is being sent to the i/o scheduler for addition to
the internal queue and later service by the driver. The request
is fully formed at this time.
Q -- queued
This notes intent to queue i/o at the given location.
No real requests exists yet.
B -- bounced
The data pages attached to this bio are not reachable
by the hardware and must be bounced to a lower memory location.
This causes a big slowdown in i/o performance, since the data
must be copied to/from kernel buffers. Usually this can be fixed
with using better hardware -- either a better i/o controller, or
a platform with an IOMMU.
M -- back merge
A previously inserted request exists that ends on the boundary of
where this i/o begins, so the i/o scheduler can merge them together.
F -- front merge
Same as the back merge, except this i/o ends where a previously
inserted requests starts.
M -- front or back merge
One of the above.
G -- get request
To send any type of request to a block device, a struct request
container must be allocated first.
S -- sleep
No available request structures were available, so the issuer has
to wait for one to be freed.
P -- plug
When i/o is queued to a previously empty block device queue,
Linux will plug the queue in anticipation of future ios being
added before this data is needed.
U -- unplug
Some request data already queued in the device, start sending
requests to the driver. This may happen automatically if a timeout
period has passed (see next entry) or if a number of requests have
been added to the queue.
T -- unplug due to timer
If nobody requests the i/o that was queued after plugging the queue,
Linux will automatically unplug it after a defined period has passed.
X -- split
On raid or device mapper setups, an incoming i/o may straddle a device
or internal zone and needs to be chopped up into smaller pieces for
service. This may indicate a performance problem due to a bad setup
of that raid/dm device, but may also just be part of normal boundary
conditions. dm is notably bad at this and will clone lots of i/o.
A -- remap
For stacked devices, incoming i/o is remapped to device below it in
the i/o stack. The remap action details what exactly is being remapped
to what.
R -- requeue
Put a request back on queue.
OPTIONS
-F typ,fmt
--format=typ,fmt
-f fmt
--format-spec=fmt
Sets output format
(See OUTPUT DESCRIPTION AND FORMATTING for details.)
The -f form specifies a format for all events
The -F form allows one to specify a format for a specific event type.
The single-character typ field is one of the action specifiers
described in ACTION IDENTIFIERS.
-A hex-mask
--set-mask=hex-mask
Set filter mask to hex-mask, see blktrace (8) for masks
-a mask
--act-mask=mask
Add mask to current filter, see blktrace (8) for masks
-D dir
--input-directory=dir
Prepend dir to input file names
-b batch
--batch={batch}
Standard input read batching
-i file
--input=file
Specifies base name for input files -- default is
device.blktrace.cpu.
As noted above, specifying -i - runs in live mode with
blktrace (reading data from standard in).
-M
--no-msgs
When -d is specified, this will stop messages from being output
to the file. (Can seriously reduce the size of the resultant file
when using the CFQ I/O scheduler.)
-h
--hash-by-name
Hash processes by name, not by PID
-o file
--output=file
Output file
-O
--no-text-output
Do not produce text output, used for binary (-d) only
-d file
--dump-binary=file
Binary output file
-q
--quiet
Quiet mode
-s
--per-program-stats
Displays data sorted by program
-t
--track-ios
Display time deltas per IO
-w span
--stopwatch=span
Display traces for the span specified -- where span can be:
end-time
-- Display traces from time 0 through end-time (in ns)
or
start:end-time
-- Display traces from time start through end-time (in ns).
-v
--verbose
More verbose marginal on marginal errors
-V
--version
Display version
OUTPUT DESCRIPTION AND FORMATTING
The output from blkparse can be tailored for specific use -- in particular, to ease parsing of output, and/or limit output fields to those the user wants to see.
The data for fields which can be output include:
a Action, a (small) string (1 or 2 characters)
c CPU id
C Command
d RWBS field, a (small) string (1-3 characters)
D 7-character string containing the major and minor numbers of
the event's device (separated by a comma).
e Error value
m Minor number of event's device.
M Major number of event's device.
n Number of blocks
N Number of bytes
p Process ID
P Display packet data -- series of hexadecimal values
s Sequence numbers
S Sector number
t Time stamp (nanoseconds)
T Time stamp (seconds)
u Elapsed value in microseconds (-t command line option)
U Payload unsigned integer
Note that the user can optionally specify field display width, and optionally a left-aligned specifier. These precede field specifiers, with a '%' character, followed by the optional left-alignment specifier (-) followed by the width (a decimal number) and then the field. Thus, to specify the command in a 12-character field that is left aligned:
-f "%-12C"
ACTION IDENTIFIERS
The following table shows the various actions which may be output:
A IO was remapped to a different device
B IO bounced
C IO completion
D IO issued to driver
F IO front merged with request on queue
G Get request
I IO inserted onto request queue
M IO back merged with request on queue
P Plug request
Q IO handled by request queue code
S Sleep request
T Unplug due to timeout
U Unplug request
X Split