RE: [EXTERNAL] Re: [PATCH] Collect both user and kernel events for autofdo tests and autoprofiledbootstrap

[Eugene Rozenfeld <Eugene.Rozenfeld@microsoft.com>]

I also set /proc/sys/kernel/perf_event_paranoid to 1 instead of the default 2.

-----Original Message-----
From: Gcc-patches <gcc-patches-bounces+erozen=microsoft.com@gcc.gnu.org> On Behalf Of Eugene Rozenfeld via Gcc-patches
Sent: Friday, June 30, 2023 2:44 PM
To: Sam James <sam@gentoo.org>; Richard Biener <richard.guenther@gmail.com>
Cc: gcc-patches@gcc.gnu.org
Subject: RE: [EXTERNAL] Re: [PATCH] Collect both user and kernel events for autofdo tests and autoprofiledbootstrap

I don't run this with elevated privileges but I set /proc/sys/kernel/kptr_restrict to 0. Setting that does require elevated privileges.

If that's not acceptable, the only fix I can think of is to make that event mapping threshold percentage a parameter to create_gcov and pass something low enough. 80% instead of the current threshold of 95% should work, although it's a bit fragile.

Eugene

-----Original Message-----
From: Sam James <sam@gentoo.org>
Sent: Friday, June 30, 2023 1:59 AM
To: Richard Biener <richard.guenther@gmail.com>
Cc: Eugene Rozenfeld <Eugene.Rozenfeld@microsoft.com>; gcc-patches@gcc.gnu.org
Subject: [EXTERNAL] Re: [PATCH] Collect both user and kernel events for autofdo tests and autoprofiledbootstrap

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Richard Biener via Gcc-patches <gcc-patches@gcc.gnu.org> writes:

> On Fri, Jun 30, 2023 at 7:28 AM Eugene Rozenfeld via Gcc-patches 
> <gcc-patches@gcc.gnu.org> wrote:
>>
>> When we collect just user events for autofdo with lbr we get some 
>> events where branch sources are kernel addresses and branch targets 
>> are user addresses. Without kernel MMAP events create_gcov can't make 
>> sense of kernel addresses. Currently create_gcov fails if it can't 
>> map at least 95% of events. We sometimes get below this threshold with just user events. The change is to collect both user events and kernel events.
>
> Does this require elevated privileges?  Can we instead "fix" create_gcov here?

Right, requiring privileges for this is going to be a no-go for a lot of builders. In a distro context, for example, it means we can't consider autofdo at all.