Re: [RFC] perf: EBNF for event syntax

[Peter Zijlstra]

On Wed, 2011-03-23 at 11:36 +0800, Lin Ming wrote:
> Hi, all
> 
> On Thu, Mar 17, 2011 at 2:02 AM, Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> wrote:
> > How about we start writing proper EBNF syntax rules for this stuff, its
> > getting seriously out of hand.
> http://marc.info/?l=linux-kernel&m=130029871318866&w=2
> 
> As Peter suggested, I wrote a simple EBNF for event syntax, as below.
> My first plan is to pass in extra config value for some events,
> for example, offcore response and load latency.
> 
> perf record -e r100b(0004):p
> 
> As above, the extra config value 0004 is passed in the parentheses.
> 
> The EBNF
> ========
> 
> EventList		:=	Event [',' EventList]

There was a suggestion a while back to make:

 -e ev1,ev2,ev3

create an event group with ev2 and ev3 siblings of ev1, and have
multiple -e instances create separate counters.

The problem is that its not backwards compatible, but something like
that would still be very nice to have.

> Event			:= 	HardwareEvent 		|
> 				RawEvent		|
> 				SoftwareEvent		|
> 				TracepointEvent		|
> 				HardwareBreakpointEvent
> 
> HardwareEvent		:=	HardwareEventName [ExtraConfig] [Modifer]
> HardwareEventName	:=	'cpu-cycles' | 'cycles' | 'instructions' /* and so on ...*/
> ExtraConfig		:=	'(' ConfigValue [',' ConfigValue] ')'
> ConfigValue		:=	HexNumber
> 
> RawEvent		:=	RawSeperator RawCode [ExtraConfig] [Modifer]
> RawSeperator		:=	'r'
> RawCode			:=	HexNumber
> 
> SoftwareEvent		:=	SoftwareEventName
> SoftwareEventName	:=	'cpu-clock' | 'task-clock' | 'faults' /* and so on ...*/
> 
> TracepointEvent		:=	SubsystemName ':' TracepointName
> SubsystemName		:=	/* All AsciiString except the pre-defined hardware/software/cache events name and BreakpointSeparator */
> TracepointName		:=	'*' | AsciiString
> 
> HardwareBreakpointEvent	:=	BreakpointSeparator BreakpointAddress [':' AccessType]
> BreakpointSeparator	:=	'mem:'
> BreakpointAddress	:=	HexNumber
> AccessType		:=	'r' | 'w' | 'x'
> 
> Modifier		:= 	ModifierSperator ModifierList
> ModifierSperator	:= 	':'
> ModifierList		:= 	ModifierItem ModifierList
> ModifierItem		:= 	{PreciseModifer} | kernelModifer | UserModifer | HypervisorModifer
> PreciseModifer		:= 	'p' /* Can be multiple PreciseModifers */
> kernelModifer		:= 	'k'
> UserModifer		:= 	'u'
> HypervisorModifer	:= 	'h'

Otherwise, very nice. Eventually we'll be able to use a parser generator
for this.

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