linux-kernel - Re: Perf trace event parse errors for KVM events

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Message-ID: <4C021D7E.1060705@redhat.com>
Date:	Sun, 30 May 2010 11:10:38 +0300
From:	Avi Kivity <avi@...hat.com>
To:	rostedt@...dmis.org
CC:	Stefan Hajnoczi <stefanha@...il.com>,
	linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, Frederic Weisbecker <fweisbec@...il.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Stefan Hajnoczi <stefanha@...ux.vnet.ibm.com>
Subject: Re: Perf trace event parse errors for KVM events

On 05/29/2010 04:19 PM, Steven Rostedt wrote:
> On Sat, 2010-05-29 at 14:50 +0300, Avi Kivity wrote:
>    
>> On 05/29/2010 12:45 AM, Steven Rostedt wrote:
>>      
>>> On Fri, 2010-05-28 at 17:42 +0100, Stefan Hajnoczi wrote:
>>>
>>>        
>>>> I get parse errors when using Steven Rostedt's trace-cmd tool, too.
>>>>
>>>> Any ideas what is going on here?  I can provide more info (e.g. trace
>>>> files) if necessary.
>>>>
>>>>          
>>> Does trace-cmd fail on the same tracepoints? Have you checkout the
>>> latest code?.
>>>
>>> I do know it fails on some of the KVM tracerpoints since the formatting
>>> they use is obnoxious.
>>>
>>>
>>>        
>> Isn't there a binary trace for this?
>>
>>      
> The pretty printing from the kernel handles this fine. But there's
> pressure to pass the format to userspace in binary and have the tool
> parse it. Currently it uses the print fmt to figure out how to parse.
>
> Using one of the examples that Stefan showed:
>
> kvmmmu/kvm_mmu_get_page: print fmt: "%s %s", ({ const char *ret =
> p->buffer + p->len; static const char *access_str[] = { "---", "--x",
> "w--", "w-x", "-u-", "-ux", "wu-", "wux" }; union kvm_mmu_page_role
> role; role.word = REC->role; trace_seq_printf(p, "sp gfn %llx %u%s q%u%s
> %s%s" " %snxe root %u %s%c", REC->gfn, role.level, role.cr4_pae ? "
> pae" : "", role.quadrant, role.direct ? " direct" : "",
> access_str[role.access], role.invalid ? " invalid" : "", role.nxe ? "" :
> "!", REC->root_count, REC->unsync ? "unsync" : "sync", 0); ret; }),
> REC->created ? "new" : "existing"
>
>
> You need a full C parser/interpreter to understand the above.
>    

Right.  The tools can fall back to %x/%s based on the structure 
descriptor if they can't parse the format string.

-- 
error compiling committee.c: too many arguments to function

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