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This patch adds a "cpumask" attribute to CCN's event_source class sysfs
directory. Perf user tool uses it to restrict events to the
processor(s) enumerated in this mask.
This patch provides a single CPU mask, making it possible to run "-a"
perf session (previously it would request the same CCN event, for
example cycle counter, on each available core and most likely fail).
Initially the mask is set to the CPU that happened to probe the driver,
but it will be changed when it is hot-un-plugged (active events are
migrated to another CPU then).
Example:
Performance counter stats for 'system wide':
CPU0 2968148 cycles
CPU1 2236736 cycles
CPU2 1797968 cycles
CPU3 1831715 cycles
CPU1 1201850868 ccn/cycles/
1.001241383 seconds time elapsed
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
56 lines
2.3 KiB
Plaintext
56 lines
2.3 KiB
Plaintext
ARM Cache Coherent Network
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==========================
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CCN-504 is a ring-bus interconnect consisting of 11 crosspoints
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(XPs), with each crosspoint supporting up to two device ports,
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so nodes (devices) 0 and 1 are connected to crosspoint 0,
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nodes 2 and 3 to crosspoint 1 etc.
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PMU (perf) driver
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-----------------
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The CCN driver registers a perf PMU driver, which provides
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description of available events and configuration options
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in sysfs, see /sys/bus/event_source/devices/ccn*.
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The "format" directory describes format of the config, config1
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and config2 fields of the perf_event_attr structure. The "events"
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directory provides configuration templates for all documented
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events, that can be used with perf tool. For example "xp_valid_flit"
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is an equivalent of "type=0x8,event=0x4". Other parameters must be
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explicitly specified. For events originating from device, "node"
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defines its index. All crosspoint events require "xp" (index),
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"port" (device port number) and "vc" (virtual channel ID) and
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"dir" (direction). Watchpoints (special "event" value 0xfe) also
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require comparator values ("cmp_l" and "cmp_h") and "mask", being
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index of the comparator mask.
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Masks are defined separately from the event description
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(due to limited number of the config values) in the "cmp_mask"
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directory, with first 8 configurable by user and additional
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4 hardcoded for the most frequent use cases.
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Cycle counter is described by a "type" value 0xff and does
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not require any other settings.
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The driver also provides a "cpumask" sysfs attribute, which contains
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a single CPU ID, of the processor which will be used to handle all
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the CCN PMU events. It is recommended that the user space tools
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request the events on this processor (if not, the perf_event->cpu value
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will be overwritten anyway). In case of this processor being offlined,
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the events are migrated to another one and the attribute is updated.
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Example of perf tool use:
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/ # perf list | grep ccn
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ccn/cycles/ [Kernel PMU event]
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<...>
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ccn/xp_valid_flit/ [Kernel PMU event]
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<...>
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/ # perf stat -a -e ccn/cycles/,ccn/xp_valid_flit,xp=1,port=0,vc=1,dir=1/ \
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sleep 1
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The driver does not support sampling, therefore "perf record" will
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not work. Per-task (without "-a") perf sessions are not supported.
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