* [PATCH 18/31] blktrace: doc: alternatives to blktrace traditional tooling
@ 2018-04-27 13:07 Steffen Maier
2018-04-27 19:40 ` Arnaldo Carvalho de Melo
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: Steffen Maier @ 2018-04-27 13:07 UTC (permalink / raw)
To: linux-btrace
Signed-off-by: Steffen Maier <maier@linux.ibm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
---
doc/blktrace.tex | 397 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 397 insertions(+)
diff --git a/doc/blktrace.tex b/doc/blktrace.tex
index 6307b9343c44..b5fc769ab891 100644
--- a/doc/blktrace.tex
+++ b/doc/blktrace.tex
@@ -256,6 +256,7 @@ You can use SCSI tracepoints instead
Correlation between blktrace and SCSI tracing:
A blktrace issue event (D) causes a scsi\_dispatch\_cmd\_start event;
a scsi\_dispatch\_cmd\_done tracepoint causes a blktrace complete event (C).
+See also Sec.~\ref{sec:form-text-outp} and Sec.~\ref{sec:block-trace-events}.
\subsection{blktrace -- post-processing}
\label{sec:blktrace-post}
@@ -370,6 +371,399 @@ Total (65,160):
...
\end{verbatim}
+\subsection{blktrace -- alternative user interfaces via ftrace}
+\label{sec:blktrace-ftrace}
+
+\subsubsection{Ftrace blk tracer}
+
+As a (mutually exclusive) alternative to the IOCTLs used by
+traditional blktrace, there is also a user interface\footnote{ v2.6.30
+ commit c71a89615411 (``blktrace: add ftrace plugin'')} based on
+sysfs and debugfs / tracefs.
+
+To use this, switch the current tracer of the ftrace kernel tracing
+infrastructure to the ``blk'' tracer:
+\begin{verbatim}
+echo blk > /sys/kernel/debug/tracing/current_tracer
+\end{verbatim}
+
+The internal trace record format is similar to traditional blktrace.
+But now the traced io actions no longer go to the relay kernel-user
+interface but instead to the kernel ftrace buffer. This means, the
+blktrace user space tool cannot record traces anymore.
+
+Suppose we want to trace block events on the first partition of a SCSI
+disk block device sda1. Things work likewise for the full block device sda.
+If the block device is not open by any means, you
+might get an error ENXIO ``No such device or address'' on trying to access
+the sysfs control interface. ``Open'' includes but is not limited to:
+filesystem in that block device mounted, block device opened directly,
+block device being part of a device-mapper (dm) table
+or of a multi-device (md) such as software RAID. For our examples with a
+block device, we use a workaround to temporarily open the device
+by means of input redirection to an unused file descriptor (42)
+limited in scope by the subshell opened by the surrounding parentheses.
+
+By default things are disabled:
+\begin{verbatim}
+% ( exec 42< /dev/sda1 ; tail /sys/block/sda/sda1/trace/* )
+=> /sys/block/sda/sda1/trace/act_mask <=
+disabled
+=> /sys/block/sda/sda1/trace/enable <=
+0
+=> /sys/block/sda/sda1/trace/end_lba <=
+disabled
+=> /sys/block/sda/sda1/trace/pid <=
+disabled
+=> /sys/block/sda/sda1/trace/start_lba <=
+disabled
+\end{verbatim}
+
+Enable full tracing for the partition:
+\begin{verbatim}
+% ( exec 42< /dev/sda1 ; echo 1 > /sys/block/sda/sda1/trace/enable )
+\end{verbatim}
+
+This enabled all block io actions, and set start and end LBA to the partition:
+\begin{verbatim}
+% ( exec 42< /dev/sda1 ; tail /sys/block/sda/sda1/trace/* )
+=> /sys/block/sda/sda1/trace/act_mask <=
+read,write,flush,sync,queue,requeue,issue,complete,fs,pc,notify,\
+ahead,meta,discard,drv_data,fua
+=> /sys/block/sda/sda1/trace/enable <=
+1
+=> /sys/block/sda/sda1/trace/end_lba <=
+1050624
+=> /sys/block/sda/sda1/trace/pid <=
+0
+=> /sys/block/sda/sda1/trace/start_lba <=
+2048
+\end{verbatim}
+Optionally writing to the sysfs attributes act\_mask, start\_lba,
+end\_lba, and pid modifies the filters.
+
+Include trace events for the SCSI command (cf.\ Sec.~\ref{sec:pc-blktrace}):
+\begin{verbatim}
+% lsscsi
+[0:0:0:1083850880]disk ... ... ... /dev/sda
+% echo "host_no=0 && channel=0 && id=0 && lun=1083850880" > \
+ /sys/kernel/debug/tracing/events/scsi/filter
+% echo 1 > /sys/kernel/debug/tracing/events/scsi/scsi_dispatch_cmd_start/enable
+% echo 1 > /sys/kernel/debug/tracing/events/scsi/scsi_dispatch_cmd_done/enable
+\end{verbatim}
+
+\begin{verbatim}
+% dd if=/dev/sda1 of=/dev/null iflag=direct count=1
+\end{verbatim}
+
+\paragraph{Formatted text output}
+\label{sec:form-text-outp}
+
+By default, the output uses the same prefix as ftrace up to and
+including the timestamp:
+
+{\footnotesize
+\begin{verbatim}
+% cat /sys/kernel/debug/tracing/trace
+# tracer: blk
+#
+ dd-15122 [001] d..1 112569.703948: 8,1 A R 2048 + 1 <- (8,1) 0
+ dd-15122 [001] d..1 112569.703963: 8,1 Q R 2048 + 1 [dd]
+ dd-15122 [001] d..1 112569.703981: 8,1 G R 2048 + 1 [dd]
+ dd-15122 [001] d..2 112569.703984: 8,1 I R 2048 + 1 [dd]
+ dd-15122 [001] d..2 112569.703987: 8,1 D R 2048 + 1 [dd]
+ dd-15122 [001] .... 112569.704011: scsi_dispatch_cmd_start: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=1 prot_sgl=0 prot_op=SCSI_PROT_NORMAL \
+cmnd=(READ_10 lba 48 txlen=1 protect=0 raw( 00 00 00 08 00 00 00 01 00)
+ <idle>-0 [000] d.s2 112569.704236: scsi_dispatch_cmd_done: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=1 prot_sgl=0 prot_op=SCSI_PROT_NORMAL \
+cmnd=(READ_10 lba 48 txlen=1 protect=0 raw( 00 00 00 08 00 00 00 01 00) \
+result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
+ <idle>-0 [000] d.s2 112569.704249: 8,1 C R 2048 + 1 [0]
+\end{verbatim}
+}
+This output format allows to use other ftrace functionality and
+options such as stacktrace.
+
+The equivalent of a manual blktrace message (see Sec.~\ref{sec:message})
+is to use the global ftrace marker functionality:
+
+{\footnotesize
+\begin{verbatim}
+% echo "hello world" > /sys/kernel/debug/tracing/trace_marker
+% cat /sys/kernel/debug/tracing/trace
+ <...>-11531 [002] .... 99702.761307: tracing_mark_write: hello world
+\end{verbatim}
+}
+
+To get an output format similar to the blkparse user space tool
+default output, enable the blk tracer option blk\_classic:
+\begin{verbatim}
+% echo blk_classic > /sys/kernel/debug/tracing/trace_options
+\end{verbatim}
+
+\begin{verbatim}
+% cat /sys/kernel/debug/tracing/trace
+# tracer: blk
+#
+# DEV CPU TIMESTAMP PID ACT FLG
+# | | | | | |
+ 8,1 1 112569.703948210 15122 A R 2048 + 1 <- (8,1) 0
+ 8,1 1 112569.703962961 15122 Q R 2048 + 1 [dd]
+ 8,1 1 112569.703980542 15122 G R 2048 + 1 [dd]
+ 8,1 1 112569.703983690 15122 I R 2048 + 1 [dd]
+ 8,1 1 112569.703986659 15122 D R 2048 + 1 [dd]
+ 0,0 1 112569.704011337 15122 U R [dd] 2882303761651335168
+Unknown action 28
+ 8,1 0 112569.704248800 0 C R 2048 + 1 [0]
+\end{verbatim}
+Currently, blk\_classic does not support sequence numbers
+(Sec.~\ref{sec:record}).
+
+If you enable other ftrace options such as SCSI trace events together
+with blk\_classic, you can get broken output or ``Unknown action
+\dots'' in the formatted text output for any event which is not
+blktrace. The ftrace buffer still contains the other events, and
+disabling blk\_classic formats these events again.
+
+\paragraph{Binary output in blktrace format}
+
+To support post-processing traces with the existing blktrace tools
+such as blkparse, the blk tracer can generate binary output in the
+format of traditional ``blktrace -o -'' (see
+Sec.~\ref{sec:live-blktrace}) on the fly when reading the ftrace
+buffer \footnote{v2.6.30 commit 08a06b83ff8b (``blkftrace: binary
+ tracing, synthesizing old format'')\newline v2.6.31 commit
+ f3948f8857ef (``blktrace: fix context-info when mixed-using blk
+ tracer and trace events'')}.
+
+\begin{verbatim}
+% echo nocontext-info > /sys/kernel/debug/tracing/trace_options
+% echo bin > /sys/kernel/debug/tracing/trace_options
+% echo blk > /sys/kernel/debug/tracing/current_tracer
+% cat /sys/kernel/debug/tracing/trace_pipe | blkparse -q -i -
+\end{verbatim}
+
+Here we intentionally do not read from trace but trace\_pipe because
+the former contains two header lines which blkparse does not expect:
+\begin{verbatim}
+# tracer: blk
+#
+\end{verbatim}
+
+\begin{verbatim}
+% dd if=/dev/sda1 iflag=direct of=/dev/null count=1
+\end{verbatim}
+
+Generating I/O causes above blkparse to output (might be batched and delayed):
+\begin{verbatim}
+ 8,0 0 0 0.000000000 14607 A R 2048 + 1 <- (8,1) 0
+ 8,1 0 0 0.000009762 14607 Q R 2048 + 1 [(null)]
+ 8,1 0 0 0.000020908 14607 G R 2048 + 1 [(null)]
+ 8,1 0 0 0.000023119 14607 I R 2048 + 1 [(null)]
+ 8,1 0 0 0.000025013 14607 D R 2048 + 1 [(null)]
+ 8,1 0 0 0.000303335 0 C R 2048 + 1 [0]
+\end{verbatim}
+
+Currently, the synthesized binary blk trace does not support: sequence
+numbers (Sec.~\ref{sec:record}), calendar time
+(Sec.~\ref{sec:timestamp}), process mapping
+(Sec.~\ref{sec:process-mapping}).
+
+\subsubsection{Block trace events}
+\label{sec:block-trace-events}
+
+Since kernel v2.6.30 and v2.6.31\footnote{2.6.30 commit 5f3ea37c7716
+ (``blktrace: port to tracepoints'')\newline v2.6.31 commit
+ 55782138e47d (``tracing/events: convert block trace points to
+ TRACE\_EVENT()'')}, the traditional blktrace shares the same trigger
+infrastructure with the new block trace events. So the following new
+block trace events provide the same information:
+
+\begin{verbatim}
+% ls -1 /sys/kernel/debug/tracing/events/block/
+block_bio_backmerge block_bio_remap block_rq_insert block_split
+block_bio_bounce block_dirty_buffer block_rq_issue block_touch_buffer
+block_bio_complete block_getrq block_rq_remap block_unplug
+block_bio_frontmerge block_plug block_rq_requeue
+block_bio_queue block_rq_complete block_sleeprq
+\end{verbatim}
+
+They use their own internal trace record format independently of
+traditional blktrace, and both can run in parallel.
+
+Block trace events can be combined with an arbitrary ftrace tracer,
+such as ``function'', as they do not need the ``blk'' tracer. They can
+also be combined with other ftrace functionality or options.
+
+To trace all io actions incl.\ SCSI command (cf.\
+Sec.~\ref{sec:pc-blktrace}) on SCSI disk sda and its partitions, we
+can filter on the device major (8) and its minors for the block events
+as well as the SCSI device HCTL identifiers for the SCSI events.
+Currently there are block events, where the device major and minor are
+always zero, e.g.\ some empty requests (RWBS value `N'), so we also
+match zero in the filter:
+\begin{verbatim}
+% lsscsi -d
+[0:0:0:1083850880]disk ... ... ... /dev/sda [8:0]
+% echo "(dev >= 0x800000 && dev <= 0x80000f) || dev = 0" > \
+ /sys/kernel/debug/tracing/events/block/filter
+% echo 1 > /sys/kernel/debug/tracing/events/block/enable
+% echo "host_no=0 && channel=0 && id=0 && lun=1083850880" > \
+ /sys/kernel/debug/tracing/events/scsi/filter
+% echo 1 > /sys/kernel/debug/tracing/events/scsi/scsi_dispatch_cmd_start/enable
+% echo 1 > /sys/kernel/debug/tracing/events/scsi/scsi_dispatch_cmd_done/enable
+\end{verbatim}
+See the kernel ftrace documentation for more details.
+
+\begin{verbatim}
+% dd if=/dev/sda1 iflag=direct of=/dev/null count=1
+\end{verbatim}
+
+{\footnotesize
+\begin{verbatim}
+% cat /sys/kernel/debug/tracing/trace
+ dd-1099 [003] .... 384.607936: block_bio_remap: 8,0 R 2048 + 1 <- (8,1) 0
+ dd-1099 [003] .... 384.607947: block_bio_queue: 8,0 R 2048 + 1 [dd]
+ dd-1099 [003] .... 384.607960: block_getrq: 8,0 R 2048 + 1 [dd]
+ dd-1099 [003] d..1 384.607964: block_rq_insert: 8,0 R 512 () 2048 + 1 [dd]
+ dd-1099 [003] d..1 384.607966: block_rq_issue: 8,0 R 512 () 2048 + 1 [dd]
+ dd-1099 [003] .... 384.607982: scsi_dispatch_cmd_start: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=1 prot_sgl=0 prot_op=SCSI_PROT_NORMAL \
+cmnd=(READ_10 lba 48 txlen=1 protect=0 raw( 00 00 00 08 00 00 00 01 00)
+ <idle>-0 [002] d.s2 384.608185: scsi_dispatch_cmd_done: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=1 prot_sgl=0 prot_op=SCSI_PROT_NORMAL \
+cmnd=(READ_10 lba 48 txlen=1 protect=0 raw( 00 00 00 08 00 00 00 01 00) \
+result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
+ <idle>-0 [002] ..s1 384.608195: block_rq_complete: 8,0 R () 2048 + 1 [0]
+ kworker/3:2-350 [003] .... 384.608826: block_getrq: 0,0 R 0 + 0 [kworker/3:2]
+ kworker/3:2-350 [003] d..1 384.608829: block_rq_insert: 0,0 N 0 () 0 + 0 [kworker/3:2]
+ kworker/3:2-350 [003] d..1 384.608830: block_rq_issue: 0,0 N 0 () 0 + 0 [kworker/3:2]
+ kworker/3:2-350 [003] .... 384.608833: scsi_dispatch_cmd_start: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=0 prot_sgl=0 prot_op=SCSI_PROT_NORMAL \
+cmnd=(TEST_UNIT_READY - raw\0 00 00 00 00 00)
+ <idle>-0 [001] d.s2 384.608949: scsi_dispatch_cmd_done: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=0 prot_sgl=0 prot_op=SCSI_PROT_NORMAL \
+cmnd=(TEST_UNIT_READY - raw\0 00 00 00 00 00) \
+result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
+ <idle>-0 [001] ..s1 384.608959: block_rq_complete: 0,0 N () 18446744073709551615 + 0 [0]
+\end{verbatim}
+}
+
+To trace and efficiently stream more events into a default output file
+trace.dat than fit into the ftrace buffer\footnote{
+ \url{git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/trace-cmd.git}}
+(cf.\ the blktrace user space tool in Sec.~\ref{sec:blktrace-post}):
+\begin{verbatim}
+% trace-cmd record -e block \
+ -f "(dev >= 0x800000 && dev <= 0x80000f) || dev = 0" \
+ -e scsi_dispatch_cmd_start \
+ -f "host_no=0 && channel=0 && id=0 && lun=1083850880" \
+ -e scsi_dispatch_cmd_done \
+ -f "host_no=0 && channel=0 && id=0 && lun=1083850880"
+Hit Ctrl^C to stop recording
+\end{verbatim}
+``trace-cmd record'' also has an option -{}-date for calendar time stamps
+(cf.\ Sec.~\ref{sec:timestamp}).
+
+Alternatively, you can use the perf tool\footnote{
+ \url{https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/perf}}
+instead of trace-cmd:
+\begin{verbatim}
+
+% perf record -a -e block:block_plug -e block:block_unplug \
+ -e "block:block_b*" --filter "(dev >= 0x800000 && dev <= 0x80000f) || dev = 0" \
+ -e "block:block_d*" --filter "(dev >= 0x800000 && dev <= 0x80000f) || dev = 0" \
+ -e "block:block_g*" --filter "(dev >= 0x800000 && dev <= 0x80000f) || dev = 0" \
+ -e "block:block_r*" --filter "(dev >= 0x800000 && dev <= 0x80000f) || dev = 0" \
+ -e "block:block_s*" --filter "(dev >= 0x800000 && dev <= 0x80000f) || dev = 0" \
+ -e "block:block_t*" --filter "(dev >= 0x800000 && dev <= 0x80000f) || dev = 0" \
+ -e scsi:scsi_dispatch_cmd_start \
+ --filter "host_no=0 && channel=0 && id=0 && lun=1083850880" \
+ -e scsi:scsi_dispatch_cmd_done \
+ --filter "host_no=0 && channel=0 && id=0 && lun=1083850880"
+\end{verbatim}
+Since we cannot specify ``block'' as subsystem but have to qualify individual
+events (optionally with wildcards), and since the (un)plug events have no
+``dev'' field to filter, we need a longer event and filter option list.
+
+Perform I/O in parallel to the recording:
+\begin{verbatim}
+% dd if=/dev/sda1 iflag=direct of=/dev/null count=1
+\end{verbatim}
+
+Stop the recording.
+
+Format the recorded report (needs at least trace-cmd-v2.4 to fully
+decode the SCSI trace events\footnote{trace-cmd-v2.4 commit
+ 3338f3c3b7c6 (``tools lib traceevent: Add scsi plugin'')}):
+
+{\footnotesize
+\begin{verbatim}
+% trace-cmd report -l
+CPU 3 is empty
+cpus=4
+ dd-1138 [000] 562.064728: block_bio_remap: 8,0 R 2048 + 1 <- (8,1) 0
+ dd-1138 [000] 562.064783: block_bio_queue: 8,0 R 2048 + 1 [dd]
+ dd-1138 [000] 562.064794: block_getrq: 8,0 R 2048 + 1 [dd]
+ dd-1138 [000] 562.064797: block_rq_insert: 8,0 R 512 () 2048 + 1 [dd]
+ dd-1138 [000] 562.064799: block_rq_issue: 8,0 R 512 () 2048 + 1 [dd]
+ dd-1138 [000] 562.064812: scsi_dispatch_cmd_start: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=1 prot_sgl=0 prot_op=0x0 \
+cmnd=(READ_10 lba 48 txlen=1 protect=0 raw( 00 00 00 08 00 00 00 01 00)
+ <idle>-0 [000] 562.064986: scsi_dispatch_cmd_done: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=1 prot_sgl=0 prot_op=0x0 \
+cmnd=(READ_10 lba 48 txlen=1 protect=0 raw( 00 00 00 08 00 00 00 01 00) \
+result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
+ <idle>-0 [000] 562.064994: block_rq_complete: 8,0 R () 2048 + 1 [0]
+ kworker/0:1-5 [000] 562.065043: block_getrq: 0,0 R 0 + 0 [kworker/0:1]
+ kworker/0:1-5 [000] 562.065045: block_rq_insert: 0,0 N 0 () 0 + 0 [kworker/0:1]
+ kworker/0:1-5 [000] 562.065046: block_rq_issue: 0,0 N 0 () 0 + 0 [kworker/0:1]
+ kworker/0:1-5 [000] 562.065049: scsi_dispatch_cmd_start: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=0 prot_sgl=0 prot_op=0x0 \
+cmnd=(TEST_UNIT_READY - raw\0 00 00 00 00 00)
+ <idle>-0 [001] 562.065163: scsi_dispatch_cmd_done: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=0 prot_sgl=0 prot_op=0x0 \
+cmnd=(TEST_UNIT_READY - raw\0 00 00 00 00 00) \
+result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
+ <idle>-0 [001] 562.065171: block_rq_complete: 0,0 N () 18446744073709551615 + 0 [0]
+\end{verbatim}
+}
+
+If you have instead used the perf tool to record:
+
+{\footnotesize
+\begin{verbatim}
+% perf script
+ dd 1193 [000] 771.144338: block:block_bio_remap: 8,0 R 2048 + 1 <- (8,1) 0
+ dd 1193 [000] 771.144347: block:block_bio_queue: 8,0 R 2048 + 1 [dd]
+ dd 1193 [000] 771.144357: block:block_getrq: 8,0 R 2048 + 1 [dd]
+ dd 1193 [000] 771.144361: block:block_rq_insert: 8,0 R 512 () 2048 + 1 [dd]
+ dd 1193 [000] 771.144364: block:block_rq_issue: 8,0 R 512 () 2048 + 1 [dd]
+ dd 1193 [000] 771.144375: scsi:scsi_dispatch_cmd_start: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=1 prot_sgl=0 prot_op=0x0 \
+cmnd=(READ_10 lba 48 txlen=1 protect=0 raw( 00 00 00 08 00 00 00 01 00)
+ swapper 0 [000] 771.144553: scsi:scsi_dispatch_cmd_done: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=1 prot_sgl=0 prot_op=0x0 \
+cmnd=(READ_10 lba 48 txlen=1 protect=0 raw( 00 00 00 08 00 00 00 01 00) \
+result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
+ swapper 0 [000] 771.144562: block:block_rq_complete: 8,0 R () 2048 + 1 [0]
+ kworker/0:1 5 [000] 771.144609: block:block_getrq: 0,0 R 0 + 0 [kworker/0:1]
+ kworker/0:1 5 [000] 771.144613: block:block_rq_insert: 0,0 N 0 () 0 + 0 [kworker/0:1]
+ kworker/0:1 5 [000] 771.144615: block:block_rq_issue: 0,0 N 0 () 0 + 0 [kworker/0:1]
+ kworker/0:1 5 [000] 771.144620: scsi:scsi_dispatch_cmd_start: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=0 prot_sgl=0 prot_op=0x0 \
+cmnd=(TEST_UNIT_READY - raw\0 00 00 00 00 00)
+ swapper 0 [001] 771.144732: scsi:scsi_dispatch_cmd_done: \
+host_no=0 channel=0 id=0 lun\x1083850880 data_sgl=0 prot_sgl=0 prot_op=0x0 \
+cmnd=(TEST_UNIT_READY - raw\0 00 00 00 00 00) \
+result=(driver=DRIVER_OK host=DID_OK message=COMMAND_COMPLETE status=SAM_STAT_GOOD)
+ swapper 0 [001] 771.144741: block:block_rq_complete: 0,0 N () 18446744073709551615 + 0 [0]
+\end{verbatim}
+}
+
+
+
%----------------------------
\newpage\section{blktrace User Guide}
\label{sec:blktrace-ug}
@@ -1022,6 +1416,7 @@ struct blk_io_trace_remap {
\label{sec:records-special}
\subsubsection{Timestamp}
+\label{sec:timestamp}
On starting tracing, blktrace writes a notification record with time
of day. The message payload consists of u32 for seconds and u32 for
@@ -1030,6 +1425,7 @@ for each trace record instead of just monotonic nanoseconds as with
the time field of struct blk\_io\_trace.
\subsubsection{Process Mapping}
+\label{sec:process-mapping}
On writing any trace record, blktrace conditionally writes a preceding
additional process record if it has not done so already for this
@@ -1044,6 +1440,7 @@ tracking list of active tracers. On trace emit, struct task\_struct of
the process remembers the current epoch.
\subsubsection{Message}
+\label{sec:message}
Text message generated via kernel call to
\texttt{blk\_add\_trace\_msg} from e.g.\ CFQ I/O scheduler, or written to
--
2.14.2
^ permalink raw reply related [flat|nested] 4+ messages in thread* Re: [PATCH 18/31] blktrace: doc: alternatives to blktrace traditional tooling
2018-04-27 13:07 [PATCH 18/31] blktrace: doc: alternatives to blktrace traditional tooling Steffen Maier
@ 2018-04-27 19:40 ` Arnaldo Carvalho de Melo
2018-05-04 16:10 ` Steffen Maier
2018-05-04 18:31 ` Arnaldo Carvalho de Melo
2 siblings, 0 replies; 4+ messages in thread
From: Arnaldo Carvalho de Melo @ 2018-04-27 19:40 UTC (permalink / raw)
To: linux-btrace
Em Fri, Apr 27, 2018 at 03:07:25PM +0200, Steffen Maier escreveu:
> Signed-off-by: Steffen Maier <maier@linux.ibm.com>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Li Zefan <lizefan@huawei.com>
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Christoph Hellwig <hch@lst.de>
Interesting, I'd suggest adding 'perf trace' to that mix, that is a strace like
perf tool that can mix and match syscalls formatted strace-like + other events,
such as tracepoints, with the record perf.data, process it later, or do it
live, like strace, but with a vastly lower overhead and not just for a workload
started from it or a pid, but supporting the other targets perf supports:
system wide, CPU wide, cgroups, etc.
For instance, to see the block lifetime of a workload that
calls fsync, intermixed to the strace like output of the 'read' and 'write'
syscalls:
[root@jouet bpf]# perf trace -e read,write,block:* dd if=/etc/passwd of=bla conv=fsync
0.054 ( 0.004 ms): dd/24556 read(fd: 3, buf: 0x7fff83d09318, count: 832 ) = 832
0.521 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.524 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.528 ( ): block:block_touch_buffer:253,2 sector\x1492603 size@96
0.534 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.550 ( 0.007 ms): dd/24556 read(buf: 0x55c3ca055000, count: 512 ) = 512
0.559 ( ): dd/24556 write(fd: 1</home/acme/bpf/bla>, buf: 0x55c3ca057000, count: 512 ) ...
0.562 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.574 ( ): block:block_dirty_buffer:253,2 sector\x18446744073709486080 size@96
0.578 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.559 ( 0.023 ms): dd/24556 ... [continued]: write()) = 512
0.584 ( 0.003 ms): dd/24556 read(buf: 0x55c3ca055000, count: 512 ) = 512
0.589 ( ): dd/24556 write(fd: 1</home/acme/bpf/bla>, buf: 0x55c3ca057000, count: 512 ) ...
0.592 ( ): block:block_dirty_buffer:253,2 sector\x18446744073709486080 size@96
0.594 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.589 ( 0.007 ms): dd/24556 ... [continued]: write()) = 512
0.598 ( 0.002 ms): dd/24556 read(buf: 0x55c3ca055000, count: 512 ) = 512
0.603 ( ): dd/24556 write(fd: 1</home/acme/bpf/bla>, buf: 0x55c3ca057000, count: 512 ) ...
0.606 ( ): block:block_dirty_buffer:253,2 sector\x18446744073709486080 size@96
0.608 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.603 ( 0.008 ms): dd/24556 ... [continued]: write()) = 512
0.613 ( 0.002 ms): dd/24556 read(buf: 0x55c3ca055000, count: 512 ) = 512
0.617 ( ): dd/24556 write(fd: 1</home/acme/bpf/bla>, buf: 0x55c3ca057000, count: 512 ) ...
0.621 ( ): block:block_dirty_buffer:253,2 sector\x18446744073709486080 size@96
0.623 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.617 ( 0.009 ms): dd/24556 ... [continued]: write()) = 512
0.629 ( 0.003 ms): dd/24556 read(buf: 0x55c3ca055000, count: 512 ) = 512
0.634 ( ): dd/24556 write(fd: 1</home/acme/bpf/bla>, buf: 0x55c3ca057000, count: 512 ) ...
0.637 ( ): block:block_dirty_buffer:253,2 sector\x18446744073709486080 size@96
0.639 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.634 ( 0.008 ms): dd/24556 ... [continued]: write()) = 512
0.644 ( 0.002 ms): dd/24556 read(buf: 0x55c3ca055000, count: 512 ) = 512
0.649 ( ): dd/24556 write(fd: 1</home/acme/bpf/bla>, buf: 0x55c3ca057000, count: 512 ) ...
0.652 ( ): block:block_dirty_buffer:253,2 sector\x18446744073709486080 size@96
0.654 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.649 ( 0.008 ms): dd/24556 ... [continued]: write()) = 512
0.659 ( 0.003 ms): dd/24556 read(buf: 0x55c3ca055000, count: 512 ) = 512
0.664 ( ): dd/24556 write(fd: 1</home/acme/bpf/bla>, buf: 0x55c3ca057000, count: 512 ) ...
0.667 ( ): block:block_dirty_buffer:253,2 sector\x18446744073709486080 size@96
0.669 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.664 ( 0.007 ms): dd/24556 ... [continued]: write()) = 512
0.674 ( 0.002 ms): dd/24556 read(buf: 0x55c3ca055000, count: 512 ) = 298
0.679 ( 0.005 ms): dd/24556 read(buf: 0x55c3ca055000, count: 512 ) = 0
0.686 ( ): dd/24556 write(fd: 1</home/acme/bpf/bla>, buf: 0x55c3ca057000, count: 298 ) ...
0.689 ( ): block:block_dirty_buffer:253,2 sector\x18446744073709486080 size@96
0.691 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.686 ( 0.008 ms): dd/24556 ... [continued]: write()) = 298
0.716 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.719 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.729 ( ): block:block_touch_buffer:253,2 sector\x1584 size@96
0.735 ( ): block:block_bio_queue:253,2 WS 63627608 + 8 [dd]
0.740 ( ): block:block_bio_remap:8,0 WS 79620440 + 8 <- (253,2) 63627608
0.743 ( ): block:block_bio_remap:8,0 WS 196985176 + 8 <- (8,6) 79620440
0.746 ( ): block:block_bio_queue:8,0 WS 196985176 + 8 [dd]
0.756 ( ): block:block_getrq:8,0 WS 196985176 + 8 [dd]
0.759 ( ): block:block_plug:[dd]
0.764 ( ): block:block_rq_insert:8,0 WS 4096 () 196985176 + 8 [dd]
0.768 ( ): block:block_unplug:[dd] 1
0.771 ( ): block:block_rq_issue:8,0 WS 4096 () 196985176 + 8 [dd]
8.864 ( 0.006 ms): dd/24556 read(buf: 0x55c3ca057910, count: 4096 ) = 2997
8.891 ( 0.003 ms): dd/24556 read(buf: 0x55c3ca057910, count: 4096 ) = 0
7+1 records in
7+1 records out
3882 bytes (3.9 kB, 3.8 KiB) copied, 0.00845109 s, 459 kB/s
8.985 ( 0.008 ms): dd/24556 write(fd: 2</dev/pts/10>, buf: 0x7fff83d07760, count: 31 ) = 31
9.013 ( 0.005 ms): dd/24556 write(fd: 2</dev/pts/10>, buf: 0x7fff83d06f90, count: 59 ) = 59
9.021 ( 0.004 ms): dd/24556 write(fd: 2</dev/pts/10>, buf: 0x7f032f1946e3, count: 1 ) = 1
[root@jouet bpf]#
If one wants instead to concentrate on the callchains leading to the block_rq_issue:
[root@jouet bpf]# perf trace --no-syscalls -e block:*rq_issue/call-graph=dwarf,max-stack\x10/ dd if=/etc/passwd of=bla conv=fsync
7+1 records in
7+1 records out
3882 bytes (3.9 kB, 3.8 KiB) copied, 0.010108 s, 384 kB/s
no symbols found in /usr/bin/dd, maybe install a debug package?
0.000 block:block_rq_issue:8,0 WS 4096 () 197218728 + 8 [dd]
blk_peek_request ([kernel.kallsyms])
fsync (/usr/lib64/libc-2.26.so)
[0xffffaa100818045d] (/usr/bin/dd)
__libc_start_main (/usr/lib64/libc-2.26.so)
[0xffffaa1008180d99] (/usr/bin/dd)
[root@jouet bpf]#
installing the debuginfo for the coreutils package, where dd lives, would give more info, etc.
Since this is an ext4 filesystem, lets add its *write* routines to the mix:
[root@jouet bpf]# perf trace --no-syscalls -e ext4:*write*/call-graph=dwarf/,block:*rq_issue/call-graph=dwarf/ dd if=/etc/passwd of=bla conv=fsync |& tail -18
0.215 ext4:ext4_da_write_pages:dev 253,2 ino 8437 first_page 1 nr_to_write 9223372036854775806 sync_mode 1
ext4_writepages ([kernel.kallsyms])
fsync (/usr/lib64/libc-2.26.so)
[0xffffa9f16310445d] (/usr/bin/dd)
__libc_start_main (/usr/lib64/libc-2.26.so)
[0xffffa9f163104d99] (/usr/bin/dd)
0.231 block:block_rq_issue:8,0 WS 4096 () 197703696 + 8 [dd]
blk_peek_request ([kernel.kallsyms])
fsync (/usr/lib64/libc-2.26.so)
[0xffffa9f16310445d] (/usr/bin/dd)
__libc_start_main (/usr/lib64/libc-2.26.so)
[0xffffa9f163104d99] (/usr/bin/dd)
0.249 ext4:ext4_writepages_result:dev 253,2 ino 8437 ret 0 pages_written 1 pages_skipped 0 sync_mode 1 writeback_index 1
ext4_writepages ([kernel.kallsyms])
fsync (/usr/lib64/libc-2.26.so)
[0xffffa9f16310445d] (/usr/bin/dd)
__libc_start_main (/usr/lib64/libc-2.26.so)
[0xffffa9f163104d99] (/usr/bin/dd)
[root@jouet bpf]#
And if we replace that --no-syscalls with *sync, we'd get as the last line this:
0.752 ( 7.651 ms): dd/24974 ... [continued]: fsync()) = 0
:-)
- Arnaldo
^ permalink raw reply [flat|nested] 4+ messages in thread* Re: [PATCH 18/31] blktrace: doc: alternatives to blktrace traditional tooling
2018-04-27 13:07 [PATCH 18/31] blktrace: doc: alternatives to blktrace traditional tooling Steffen Maier
2018-04-27 19:40 ` Arnaldo Carvalho de Melo
@ 2018-05-04 16:10 ` Steffen Maier
2018-05-04 18:31 ` Arnaldo Carvalho de Melo
2 siblings, 0 replies; 4+ messages in thread
From: Steffen Maier @ 2018-05-04 16:10 UTC (permalink / raw)
To: linux-btrace
On 04/27/2018 09:40 PM, Arnaldo Carvalho de Melo wrote:
> Em Fri, Apr 27, 2018 at 03:07:25PM +0200, Steffen Maier escreveu:
>> Signed-off-by: Steffen Maier <maier@linux.ibm.com>
>> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
>> Cc: Li Zefan <lizefan@huawei.com>
>> Cc: Steven Rostedt <rostedt@goodmis.org>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Peter Zijlstra <peterz@infradead.org>
>> Cc: Christoph Hellwig <hch@lst.de>
>
> Interesting, I'd suggest adding 'perf trace' to that mix, that is a strace like
> perf tool that can mix and match syscalls formatted strace-like + other events,
Thanks for the feedback!
Indeed, I looked at its man page but should have kept reading, because I
stopped when I saw strace and thus missed that it can also handle other
events.
> such as tracepoints, with the record perf.data, process it later, or do it
I tried to use "perf trace" with -i and perf.data from a previous "perf
record" for offline analysis, but I must be doing something wrong:
# perf trace -i perf.data
<<gets me into a pager with no content>>
# perf trace -v -i perf.data --no-syscalls
Please specify something to trace.
Is it because my perf.data does not contain any raw_syscall events?
Whereas "perf script" formats the trace sequence of perf.data.
> live, like strace, but with a vastly lower overhead and not just for a workload
Cool, I have to remember this for other future analysis cases.
> started from it or a pid, but supporting the other targets perf supports:
> system wide, CPU wide, cgroups, etc.
>
> For instance, to see the block lifetime of a workload that
> calls fsync, intermixed to the strace like output of the 'read' and 'write'
> syscalls:
>
> [root@jouet bpf]# perf trace -e read,write,block:* dd if=/etc/passwd of=bla conv=fsync
> 0.735 ( ): block:block_bio_queue:253,2 WS 63627608 + 8 [dd]
> 0.740 ( ): block:block_bio_remap:8,0 WS 79620440 + 8 <- (253,2) 63627608
> 0.743 ( ): block:block_bio_remap:8,0 WS 196985176 + 8 <- (8,6) 79620440
> 0.746 ( ): block:block_bio_queue:8,0 WS 196985176 + 8 [dd]
> 0.756 ( ): block:block_getrq:8,0 WS 196985176 + 8 [dd]
> 0.759 ( ): block:block_plug:[dd]
> 0.764 ( ): block:block_rq_insert:8,0 WS 4096 () 196985176 + 8 [dd]
> 0.768 ( ): block:block_unplug:[dd] 1
> 0.771 ( ): block:block_rq_issue:8,0 WS 4096 () 196985176 + 8 [dd]
Using process filter, by design means that complete events would only be
traced if they happen to occur when the same process was scheduled.
Since they occur in IRQ context, it's often another process. For use
cases as yours, that's likely not a problem.
For my cases, where I want to see every related block event, I usually
use option -a for full system.
The "perf trace" v4.16 I tried, does not seem to accept event filters
and the man page also does not mention such option. In order to separate
system events (e.g. syslog I/O or paging) from the workload events I'm
interested in, I would need some event filtering I guess. Unless I did
something wrong, "perf trace" seems currently further away from how
traditional blktrace tooling works.
This is roughly where I came from when writing up my things:
Dimensions:
* type: I/O actions, block events
* size: record to memory buffer, stream from memory buffer
* analysis: online (live trace), offline (efficiently record/stream and
then show later)
* filters: blktrace always filters for device(s), also need for events
Due to time and space constraints, I don't cover all possible combinations.
E.g. for block events, I only cover:
* manual setup and manually reading from ftrace buffer, and
* efficient streaming of traces for offline analysis.
I.e. no "streamed" live tracing.
> If one wants instead to concentrate on the callchains leading to the block_rq_issue:
>
> [root@jouet bpf]# perf trace --no-syscalls -e block:*rq_issue/call-graph=dwarf,max-stack\x10/ dd if=/etc/passwd of=bla conv=fsync
> 7+1 records in
> 7+1 records out
> 3882 bytes (3.9 kB, 3.8 KiB) copied, 0.010108 s, 384 kB/s
> no symbols found in /usr/bin/dd, maybe install a debug package?
> 0.000 block:block_rq_issue:8,0 WS 4096 () 197218728 + 8 [dd]
> blk_peek_request ([kernel.kallsyms])
> fsync (/usr/lib64/libc-2.26.so)
> [0xffffaa100818045d] (/usr/bin/dd)
> __libc_start_main (/usr/lib64/libc-2.26.so)
> [0xffffaa1008180d99] (/usr/bin/dd)
> [root@jouet bpf]#
I was hoping to cover all additional functionality by referring the
reader to the respective documentation elsewhere and keep the blktrace
docs somewhat limited in scope (also to avoid duplication):
+See the kernel ftrace documentation for more details.
[I also use filtered (kernel) stacktraces and other functionality when I
use ftrace for analysis or understanding code.]
> installing the debuginfo for the coreutils package, where dd lives, would give more info, etc.
that is very nice
I try to come up with a short reference to "perf trace" in my text to
provide the reader with an idea of what's possible beyond blktrace.
Do the other perf use cases in my patch make sense or did I get anything
wrong from a review point of view?
--
Mit freundlichen Grüßen / Kind regards
Steffen Maier
Linux on z Systems Development
IBM Deutschland Research & Development GmbH
Vorsitzende des Aufsichtsrats: Martina Koederitz
Geschaeftsfuehrung: Dirk Wittkopp
Sitz der Gesellschaft: Boeblingen
Registergericht: Amtsgericht Stuttgart, HRB 243294
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 18/31] blktrace: doc: alternatives to blktrace traditional tooling
2018-04-27 13:07 [PATCH 18/31] blktrace: doc: alternatives to blktrace traditional tooling Steffen Maier
2018-04-27 19:40 ` Arnaldo Carvalho de Melo
2018-05-04 16:10 ` Steffen Maier
@ 2018-05-04 18:31 ` Arnaldo Carvalho de Melo
2 siblings, 0 replies; 4+ messages in thread
From: Arnaldo Carvalho de Melo @ 2018-05-04 18:31 UTC (permalink / raw)
To: linux-btrace
Em Fri, May 04, 2018 at 06:10:38PM +0200, Steffen Maier escreveu:
> On 04/27/2018 09:40 PM, Arnaldo Carvalho de Melo wrote:
> > Em Fri, Apr 27, 2018 at 03:07:25PM +0200, Steffen Maier escreveu:
> > > Signed-off-by: Steffen Maier <maier@linux.ibm.com>
> > > Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> > > Cc: Li Zefan <lizefan@huawei.com>
> > > Cc: Steven Rostedt <rostedt@goodmis.org>
> > > Cc: Ingo Molnar <mingo@redhat.com>
> > > Cc: Peter Zijlstra <peterz@infradead.org>
> > > Cc: Christoph Hellwig <hch@lst.de>
> >
> > Interesting, I'd suggest adding 'perf trace' to that mix, that is a strace like
> > perf tool that can mix and match syscalls formatted strace-like + other events,
>
> Thanks for the feedback!
>
> Indeed, I looked at its man page but should have kept reading, because I
> stopped when I saw strace and thus missed that it can also handle other
> events.
>
> > such as tracepoints, with the record perf.data, process it later, or do it
>
> I tried to use "perf trace" with -i and perf.data from a previous "perf
> record" for offline analysis, but I must be doing something wrong:
>
> # perf trace -i perf.data
> <<gets me into a pager with no content>>
Right... the code to handle non raw_syscalls was added after the offline
analysis part, so probably 'perf trace -i perf.data' has issues with
non-raw_syscalls...
> # perf trace -v -i perf.data --no-syscalls
> Please specify something to trace.
>
> Is it because my perf.data does not contain any raw_syscall events?
>
> Whereas "perf script" formats the trace sequence of perf.data.
Right.
> > live, like strace, but with a vastly lower overhead and not just for a workload
>
> Cool, I have to remember this for other future analysis cases.
>
> > started from it or a pid, but supporting the other targets perf supports:
> > system wide, CPU wide, cgroups, etc.
> >
> > For instance, to see the block lifetime of a workload that
> > calls fsync, intermixed to the strace like output of the 'read' and 'write'
> > syscalls:
> >
> > [root@jouet bpf]# perf trace -e read,write,block:* dd if=/etc/passwd of=bla conv=fsync
>
> > 0.735 ( ): block:block_bio_queue:253,2 WS 63627608 + 8 [dd]
> > 0.740 ( ): block:block_bio_remap:8,0 WS 79620440 + 8 <- (253,2) 63627608
> > 0.743 ( ): block:block_bio_remap:8,0 WS 196985176 + 8 <- (8,6) 79620440
> > 0.746 ( ): block:block_bio_queue:8,0 WS 196985176 + 8 [dd]
> > 0.756 ( ): block:block_getrq:8,0 WS 196985176 + 8 [dd]
> > 0.759 ( ): block:block_plug:[dd]
> > 0.764 ( ): block:block_rq_insert:8,0 WS 4096 () 196985176 + 8 [dd]
> > 0.768 ( ): block:block_unplug:[dd] 1
> > 0.771 ( ): block:block_rq_issue:8,0 WS 4096 () 196985176 + 8 [dd]
>
> Using process filter, by design means that complete events would only be
> traced if they happen to occur when the same process was scheduled. Since
> they occur in IRQ context, it's often another process. For use cases as
> yours, that's likely not a problem.
Right, to handle IRQ context it would require something more
sophisticated to probably use eBPF to attach to those tracepoints and
use more than just process context to filter what should be
considered...
> For my cases, where I want to see every related block event, I usually use
> option -a for full system.
Right, using eBPF like this super simple use case to filter at the
origin, i.e. at tracepoint time, in-kernel, would help:
[root@jouet perf]# cat tools/perf/examples/bpf/5sec.c
#include <bpf.h>
SEC("func=hrtimer_nanosleep rqtp->tv_sec")
int func(void *ctx, int err, long sec)
{
return sec = 5;
}
license(GPL);
[root@jouet perf]#
^C[root@jouet perf]# perf trace --no-syscalls -e tools/perf/examples/bpf/5sec.c/call-graph=dwarf/
0.000 perf_bpf_probe:func:(ffffffff9811b5f0) tv_sec=5
hrtimer_nanosleep ([kernel.kallsyms])
__x64_sys_nanosleep ([kernel.kallsyms])
do_syscall_64 ([kernel.kallsyms])
entry_SYSCALL_64 ([kernel.kallsyms])
__GI___nanosleep (/usr/lib64/libc-2.26.so)
rpl_nanosleep (/usr/bin/sleep)
xnanosleep (/usr/bin/sleep)
main (/usr/bin/sleep)
__libc_start_main (/usr/lib64/libc-2.26.so)
_start (/usr/bin/sleep)
^C[root@jouet perf]#
The above is for a kprobe, unrelated function, but could be for a block
tracepoint, etc. I.e. the filtering you do post processing would be done
as the tracepoints hit, would require setting up some eBPF maps, etc.
> The "perf trace" v4.16 I tried, does not seem to accept event filters and
> the man page also does not mention such option. In order to separate system
> events (e.g. syslog I/O or paging) from the workload events I'm interested
> in, I would need some event filtering I guess. Unless I did something wrong,
> "perf trace" seems currently further away from how traditional blktrace
> tooling works.
sure, blktrace is a specialized tool just for block tracing :-)
> This is roughly where I came from when writing up my things:
>
> Dimensions:
> * type: I/O actions, block events
> * size: record to memory buffer, stream from memory buffer
> * analysis: online (live trace), offline (efficiently record/stream and then
> show later)
> * filters: blktrace always filters for device(s), also need for events
>
> Due to time and space constraints, I don't cover all possible combinations.
Right
> E.g. for block events, I only cover:
> * manual setup and manually reading from ftrace buffer, and
> * efficient streaming of traces for offline analysis.
> I.e. no "streamed" live tracing.
>
> > If one wants instead to concentrate on the callchains leading to the block_rq_issue:
> >
> > [root@jouet bpf]# perf trace --no-syscalls -e block:*rq_issue/call-graph=dwarf,max-stack\x10/ dd if=/etc/passwd of=bla conv=fsync
> > 7+1 records in
> > 7+1 records out
> > 3882 bytes (3.9 kB, 3.8 KiB) copied, 0.010108 s, 384 kB/s
> > no symbols found in /usr/bin/dd, maybe install a debug package?
> > 0.000 block:block_rq_issue:8,0 WS 4096 () 197218728 + 8 [dd]
> > blk_peek_request ([kernel.kallsyms])
> > fsync (/usr/lib64/libc-2.26.so)
> > [0xffffaa100818045d] (/usr/bin/dd)
> > __libc_start_main (/usr/lib64/libc-2.26.so)
> > [0xffffaa1008180d99] (/usr/bin/dd)
> > [root@jouet bpf]#
>
> I was hoping to cover all additional functionality by referring the reader
> to the respective documentation elsewhere and keep the blktrace docs
> somewhat limited in scope (also to avoid duplication):
>
> +See the kernel ftrace documentation for more details.
>
> [I also use filtered (kernel) stacktraces and other functionality when I use
> ftrace for analysis or understanding code.]
>
> > installing the debuginfo for the coreutils package, where dd lives, would give more info, etc.
>
> that is very nice
>
> I try to come up with a short reference to "perf trace" in my text to
> provide the reader with an idea of what's possible beyond blktrace.
>
> Do the other perf use cases in my patch make sense or did I get anything
> wrong from a review point of view?
I don't remember any problems with your text :-)
- Arnaldo
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2018-04-27 13:07 [PATCH 18/31] blktrace: doc: alternatives to blktrace traditional tooling Steffen Maier
2018-04-27 19:40 ` Arnaldo Carvalho de Melo
2018-05-04 16:10 ` Steffen Maier
2018-05-04 18:31 ` Arnaldo Carvalho de Melo
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