linux-kernel - Re: [PATCH 1/5] perf trace: add support for pagefault tracing

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Date:	Thu, 19 Jun 2014 16:06:52 +0400
From:	Stanislav Fomichev <stfomichev@...dex-team.ru>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	a.p.zijlstra@...llo.nl, paulus@...ba.org, mingo@...hat.com,
	dsahern@...il.com, jolsa@...hat.com,
	xiaoguangrong@...ux.vnet.ibm.com, yangds.fnst@...fujitsu.com,
	adrian.hunter@...el.com, namhyung@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] perf trace: add support for pagefault tracing

> So make it default to the most common case :-)
Ok, agreed, will make --pf=all|maj|min and will default it to maj.

> That is my expectation, yes, if I ask for the map where address N is, it
> should return just that, where have you found this bug?
> 
> The thread__find_addr_map will end up calling maps__find() and it does
> this:
> 
>                 if (ip < m->start)
>                         p = &(*p)->rb_left;
>                 else if (ip > m->end)
>                         p = &(*p)->rb_right;
>                 else
>                         return m;
> 
> Where is the problem?
You're right, we don't need to check the range, if map is non-null it's a
valid one. I'll remove valid_dso and will just check al.map for null.

> Understood the intent, but the test here is really:
> 
> 		if (evsel->attr.type == PERF_TYPE_TRACEPOINT &&
> 		    sample.raw_data == NULL)
> 
> Ok?
Yes, makes more sense.

> Also, have you considered using:
> 
> [root@zoo ~]# perf list exceptions:page_fault*
>   exceptions:page_fault_user                         [Tracepoint event]
>   exceptions:page_fault_kernel                       [Tracepoint event]
> [root@zoo ~]#
> 
> Instead? I need to check if they're completely equivalent to what we
> need here...
Hm, didn't know there are two kinds of fault events :-/
But it seems these are x86 only.
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