On Mon, Feb 10, 2020 at 12:56:18PM -0800, Greg KH wrote:
> On Mon, Feb 10, 2020 at 11:47:49AM +0800, Wu Hao wrote:
> > +What: /sys/bus/event_source/devices/fmeX/format
> > +Date: February 2020
> > +KernelVersion: 5.7
> > +Contact: Wu Hao <hao.wu@xxxxxxxxx>
> > +Description: Read-only. Attribute group to describe the magic bits
> > + that go into perf_event_attr.config for a particular pmu.
> > + (See ABI/testing/sysfs-bus-event_source-devices-format).
> > +
> > + Each attribute under this group defines a bit range of the
> > + perf_event_attr.config. All supported attributes are listed
> > + below.
> > +
> > + event = "config:0-11" - event ID
> > + evtype = "config:12-15" - event type
> > + portid = "config:16-23" - event source
> > +
> > + For example,
> > +
> > + fab_mmio_read = "event=0x06,evtype=0x02,portid=0xff"
>
> Are perf sysfs files always this bad "multiple values per file"? Or is
> that unique to this driver? If not unique, do you have specific
> examples in the kernel that currently do this today?
Hi Greg,
Thanks a lot for the review. : )
Perf sysfs files allow this kind of output, so some perf drivers are using
the similar format for their jobs.
Examples from my machine.
# cat /sys/bus/event_source/devices/cpu/events/cycles-ct
event=0x3c,in_tx=1,in_tx_cp=1
# cat /sys/bus/event_source/devices/cpu/events/el-start
event=0xc8,umask=0x1
# cat /sys/bus/event_source/devices/cpu/events/instructions
event=0xc0
# cat /sys/bus/event_source/devices/cpu/events/branch-instructions
event=0xc4
See arch/x86/events/intel/core.c
EVENT_ATTR_STR(cycles-ct, cycles_ct, "event=0x3c,in_tx=1,in_tx_cp=1");
...
And descriptions/examples from ABI/testing/sysfs-bus-event_source-devices-events
What: /sys/bus/event_source/devices/<pmu>/events/<event>
Date: 2014/02/24
Contact: Linux kernel mailing list <linux-kernel@xxxxxxxxxxxxxxx>
Description: Per-pmu performance monitoring events specific to the running system
Each file (except for some of those with a '.' in them, '.unit'
and '.scale') in the 'events' directory describes a single
performance monitoring event supported by the <pmu>. The name
of the file is the name of the event.
File contents:
<term>[=<value>][,<term>[=<value>]]...
Where <term> is one of the terms listed under
/sys/bus/event_source/devices/<pmu>/format/ and <value> is
a number is base-16 format with a '0x' prefix (lowercase only).
If a <term> is specified alone (without an assigned value), it
is implied that 0x1 is assigned to that <term>.
Examples (each of these lines would be in a seperate file):
event=0x2abc
event=0x423,inv,cmask=0x3
domain=0x1,offset=0x8,starting_index=0xffff
domain=0x1,offset=0x8,core=?
Each of the assignments indicates a value to be assigned to a
particular set of bits (as defined by the format file
corresponding to the <term>) in the perf_event structure passed
to the perf_open syscall.
In the case of the last example, a value replacing "?" would
need to be provided by the user selecting the particular event.
This is referred to as "event parameterization". Event
parameters have the format 'param=?'.
So this is not something new introduced by this patch.
>
>
> > +static struct attribute *fme_perf_events_attrs_empty[] = {
> > + NULL,
>
> Huh?
>
> > +};
> > +
> > +static struct attribute_group fme_perf_events_group = {
> > + .name = "events",
> > + .attrs = fme_perf_events_attrs_empty,
>
> You create an empty directory? Why? What goes in here?
>
> very odd...
Actually events are filled into this "events" from several different groups
via pmu->attr_update[1].
pmu->attr_update = fme_perf_events_groups;
pmu->attr_update allows us to update "events" directories with attributes that
depend on various HW conditions. In our case, several different groups with
different is_visible functions are filled into "events" using this method.
And several existing pmu drivers (e.g. arch/x86/events/intel/cstate.c) are
using the same way (having an empty directory first and update it using
pmu->attr_update).
But I have to admit that I should add some comments there to avoid confusion,
sorry, will do that in the next version.
[1] https://lkml.org/lkml/2019/5/4/188
Thanks
Hao
>
> greg k-h
