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dax_dtrace(3dax)
dax_dtrace(3DAX) DAX Library Functions dax_dtrace(3DAX)
NAME
dax_dtrace - DTrace probes for libdax
DESCRIPTION
The libdax library defines the following DTrace SDT probes. The
provider name is dax.
dax-post
This probe is called when any of the dax_post_xxxx() functions post a
request to DAX. If a function posts multiple DAX requests, this probe
is called for each request.
The arguments for this probe are as follows:
arg0 is dax_context_t * Context passed to the post function
arg1 is dax_queue_t * Queue passed to the post function
arg2 is uint64_t udata passed to the post function
dax-execute
This probe is called when a non-post DAX function completes.
The arguments for this probe are as follows:
arg0 is uint64_t A filter word that contains a small
amount of data describing the command.
You can use it in a filter expression,
without incurring the cost of a copyin.
The filter word has the following format:
Bits: 63-32 31-24 23-16 15-0
Field: reserved major minor cmd
cmd is the DAX command that executed,
with values from dax_cmd_t. You can ac‐
cess this sub-field by using the
DAX_DFILTER_CMD(filter) convenience
macro.
major is the major version of the API
used by the ctx that generated this
probe. You can access this sub-field by
using the DAX_DFILTER_MAJOR(filter) con‐
venience macro.
minor is the minor version of the API
used by the ctx that generated this
probe. You can access this sub-field by
using the DAX_DFILTER_MINOR(filter) con‐
venience macro.
arg1 is dax_request_t * Structure that describes the operation
arg2 is dax_result_t * Structure that describes the result of
the operation
arg3 is dax_perf_event_t * Structure that describes the performance
events that occurred during this opera‐
tion
dax-poll
This probe is called when a DAX post function completes asynchronously.
The argument types and definitions are identical to the dax-execute
probe.
dax_request_t Structure
This structure contains the arguments passed to the libdax function
that called the probe. The description of the arguments are:
major and minor The version of the API used by the ctx that gener‐
ated this probe
ctx DAX context passed to the libdax function that
called the probe
flags The flags argument passed to the function
udata The udata argument passed to the post function, or
NULL for a non-post function. If udata is unique per
request, you can use it in the script as an index
into an associative array to track information re‐
lated to the request, such as a starting timestamp.
queue The queue argument passed to the post function, or
NULL for a non-post function
cmd Indicates the type of the command that executed. The
following table shows which fields are valid for
each value of cmd.
tab(); lw(NaNi) lw(NaNi) lw(NaNi) lw(NaNi) cmdFields
DAX_CMD_SCAN_VALUEsrc, dst, scan_value
DAX_CMD_SCAN_RANGEsrc, dst, scan_range
DAX_CMD_TRANSLATEsrc, dst, translate DAX_CMD_SELECT‐
src, dst, select DAX_CMD_EXTRACTsrc, dst
DAX_CMD_COPYcopy DAX_CMD_FILLfill DAX_CMD_ANDsrc,
src2, dst DAX_CMD_ORsrc, src2, dst DAX_CMD_XORsrc,
src2, dst
dax_perf_event_t Structure
This structure contains the performance events. The description of the
performance events is as follows:
page Number of physical pages that were crossed during the exe‐
cution of the function. Each crossing causes an additional
command to be submitted to DAX.
You can reduce crossings by mapping buffers with larger
pages. For more information, see the MC_HAT_ADVISE option
of memcntl(2).
retry Number of times command was re-submitted because of tran‐
sient resource contention. This is usually 0, but may in‐
crease because of high system load.
emulate Has the value 1 if some or all of the command failed to
run on DAX and was emulated in software, else 0. Emulation
of commands occurs in conditions such as transient re‐
source contention, to guarantee completion.
nomap Number of times this command was re-submitted because a
buffer address was not translatable, else 0. This is usu‐
ally 0, but may increase because of high system load.
copy Has the value 1 if the command uses an intermediate source
or destination buffer. This can occur in page crossing
commands and commands that are long because of DAX align‐
ment restrictions.
unzip Has the value 1 if the command unzipped the src into a
temporary buffer. This can occur in page crossing commands
and commands that are long because of DAX alignment re‐
strictions.
split Number of times a long command was split at the maximum
size supported by DAX and submitted as multiple hardware
commands.
Splitting of a command happens because its src vector or
its dst vector is too long. The max_src_len and
max_dst_len values in the dax_get_props() function define
the length of the src and dst vectors.
Splitting of a command does not affect its functionality,
but sometimes reduces its efficiency when compared to ex‐
plicitly passing multiple shorter vectors. If the copy or
unzip event is non-zero, you can improve the performance
by passing shorter vectors.
cycles Number of cycles DAX spent executing the command, exclud‐
ing queueing delay and command fetching time.
frequency DAX frequency, in MHz.
EXAMPLES
The following example shows how to run the dax.d D script that displays
various events for each DAX command listed in the script.
The dax.d D script is as follows.
#include <dax.h>
#pragma D option quiet
#define PRINT_COMMAND(i) \
printf("%10s %7d %9d %9d %5d %5d %5d %5d %5d %5d %3d\n",\
Cmd[i], Count[i], Elements[i], Events[i].cycles, \
Events[i].page, Events[i].split, Events[i].unzip, \
Events[i].copy, Events[i].retry, Events[i].nomap, \
Events[i].emulate)
#define END_COMMAND(cmd) \
dtrace:::END \
/ Count[cmd] != 0 / \
{ \
PRINT_COMMAND(cmd); \
}
dax_perf_event_t Events[10];
long Elements[10];
long Count[10];
dtrace:::BEGIN
{
Cmd[DAX_CMD_SCAN_VALUE] = "scan_value";
Cmd[DAX_CMD_SCAN_RANGE] = "scan_range";
Cmd[DAX_CMD_TRANSLATE] = "translate";
Cmd[DAX_CMD_SELECT] = "select";
Cmd[DAX_CMD_EXTRACT] = "extract";
Cmd[DAX_CMD_COPY] = "copy";
Cmd[DAX_CMD_FILL] = "fill";
Cmd[DAX_CMD_AND] = "and";
Cmd[DAX_CMD_OR] = "or";
Cmd[DAX_CMD_XOR] = "xor";
}
dax$target:::dax-execute,
dax$target:::dax-poll
{
cmd = DAX_DFILTER_CMD(arg0);
req = (dax_request_t *) copyin(arg1, sizeof(dax_request_t));
res = (dax_result_t *) copyin(arg2, sizeof(dax_result_t));
ev = (dax_perf_event_t *) copyin(arg3, sizeof(dax_perf_event_t));
Count[cmd]++;
elements = (cmd == DAX_CMD_COPY ? req->arg.copy.count :
(cmd == DAX_CMD_FILL ? req->arg.fill.count :
req->src.elements));
Elements[cmd] += elements;
Events[cmd].frequency = ev->frequency;
Events[cmd].cycles += ev->cycles;
Events[cmd].page += ev->page;
Events[cmd].emulate += ev->emulate;
Events[cmd].nomap += ev->nomap;
Events[cmd].copy += ev->copy;
Events[cmd].retry += ev->retry;
Events[cmd].split += ev->split;
Events[cmd].unzip += ev->unzip;
}
dtrace:::END
{
printf("%10s %7s %9s %9s %5s %5s %5s %5s %5s %5s %3s\n",
"command", "count", "elems", "cycles", "cross", "split",
"unzip", "copy", "retry", "nomap", "em");
}
END_COMMAND(DAX_CMD_SCAN_VALUE)
END_COMMAND(DAX_CMD_SCAN_RANGE)
END_COMMAND(DAX_CMD_TRANSLATE)
END_COMMAND(DAX_CMD_SELECT)
END_COMMAND(DAX_CMD_EXTRACT)
END_COMMAND(DAX_CMD_COPY)
END_COMMAND(DAX_CMD_FILL)
END_COMMAND(DAX_CMD_AND)
END_COMMAND(DAX_CMD_OR)
END_COMMAND(DAX_CMD_XOR)
To run the dax.d D script, use the following commands:
# DAX_DEBUG_OPTIONS=perf; export DAX_DEBUG_OPTIONS
# dtrace -Cs dax.d -I$inc -c a.out
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Availabilitysystem/library _ Interface StabilityCommit‐
ted
SEE ALSO
libdax(3LIB), dax_get_props(3DAX)
Oracle Solaris 11.4 17 Aug 2017 dax_dtrace(3DAX)