linux-kernel - Re: [PATCH v24b] RAS: Add a tracepoint for reporting memory controller events

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Date:	Fri, 18 May 2012 14:27:10 -0300
From:	Mauro Carvalho Chehab <mchehab@...hat.com>
To:	Borislav Petkov <bp@...64.org>
CC:	Ingo Molnar <mingo@...nel.org>,
	Linux Edac Mailing List <linux-edac@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Aristeu Rozanski <arozansk@...hat.com>,
	Doug Thompson <norsk5@...oo.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH v24b] RAS: Add a tracepoint for reporting memory controller
 events

Em 18-05-2012 13:40, Borislav Petkov escreveu:
> On Fri, May 18, 2012 at 11:31:46AM -0300, Mauro Carvalho Chehab wrote:
>> Ok, but you won't use trace_sched_switch() as a memory tracepoint, as
>> they represent different things.
>>
>> Memory errors are different than CPU errors. So, their tracepoints
>> will be different.
> 
> WTF? A tracepoint is a tracepoint.

This is the event you've mentioned:

TRACE_EVENT(sched_switch,

	TP_PROTO(struct task_struct *prev,
		 struct task_struct *next),

It doesn't have the same arguments of a memory tracepoint, like:

TRACE_EVENT(mm_vmscan_wakeup_kswapd,

	TP_PROTO(int nid, int zid, int order),

trace events for different things will have different arguments.

> 
>>> Right, and this is why I'm asking you to have the following tracepoint proto:
>>>
>>> +       TP_PROTO(const unsigned int err_type,
>>> +                const unsigned int mc_index,
>>> +                const char *error_msg,
>>> +                const char *label,
>>> +                const char *location,
>>> +                const char *detail)
>>>
>>> where detail contains all the crap one driver adds for technical people
>>> to pinpoint where the error is.
>>>
>>> And not have _TWO_ detail arguments!
>>
>> And what I'm saying is that this should be, instead:
>>
>> + TP_PROTO(const unsigned int err_type,
>> +          const unsigned int mc_index,
>> +          const char *error_msg,
>> +          const char *label,
>> +          int layer0,
>> +          int layer1,
>> +          int layer2,
>> +          unsigned long pfn,
>> +          unsigned long offset,
>> +          unsigned long grain,
>> +          unsigned long syndrome,
>> +          const char *driver_detail),
>>
>> So, having just one detail argument, filled by the driver, and not
>> folding "location" and core "details" into strings, but keeping as they
>> are.
> 
> And this way you're enforcing an interface that all drivers will have
> to adhere to. What if "grain" doesn't mean a thing for a driver,  or
> "syndrome" or whatever? What if some other entity wants to use that
> tracepoint?

This enforcement is already there at the EDAC API/ABI. This patch series
won't change that.

Memory controllers that can't get the error address (page/offset/grain)
or the syndrome fills those information with 0.

Maybe there is a driver deficiency (or a bad hardware implementation) 
that would not allow to report where the error happened, but that doesn't
mean that we should create a crappy API due to bad hardware.

> 
> See what I'm sayin?
> 
> Having
> 
>        TP_PROTO(const unsigned int err_type,
>                 const unsigned int mc_index,
>                 const char *error_msg,
>                 const char *label,
>                 const char *location,
>                 const char *detail)
> 
> is a bit more generic and userspace can parse it however it likes.
> 
> Actually, I'd slim this up even more:
> 
>        TP_PROTO(const unsigned int mc_index,
>                 const char *error_msg,
>                 const char *label,
>                 const char *location,
>                 const char *detail)

Well, this even more generic:
	TP_PROTO(const char *msg)

but the more we convert other fields into strings, the harder is for
userspace to handle it, as fields may be on different order, string
conversion patches might change or break the parsing behavior, 
different drivers will require different parsing expressions, etc.

> and have error_msg contain the "Corrected/Uncorrected/Fatal" things
> and this way you can drop all the ternary operators in the tracepoint
> definition.
> 
>>> Btw, the output looks like this here:
>>>
>>>            <...>-2723  [001] .N..    89.107045: mc_event: Corrected error: on memory stick "unknown memory" (mc:0 csrow:3 channel:1 page:0x5bac7 offset:0x388 grain:0 syndrome:0xfc5b driver:amd64_edac)
>>>
>>> Come to think of it, the "driver:amd64_edac" is not really needed
>>> because on every single system there's only one EDAC driver running and
>>> I don't think the fact that we're telling in the tracepoint who detected
>>> the error is meaningfull information.
>>>
>>> Which means, you can remove the EDAC_MOD_STR argument you're passing to
>>> edac_mc_handle_error() and have one less argument.
>>
>> That's what I said you, but you didn't seem to agree, as I understood that
>> you've required to keep "amd64_edac"  at the trace, due to:
>> 	http://markmail.org/message/nr3ooep7gc7mhgdl.
>>
>> If you're ok, I'll remove EDAC_MOD_STR argument from the amd64_edac calls
>> on a separate patch (with can be merged latter with the patch that converted
>> amd64_edac to the new function calls).
> 
> Ok.

Ok, I'll prepare a patch for it after we finish discussing this patch.

Regards,
Mauro
> 

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