RE: [EXTERNAL] Re: State of AutoFDO in GCC

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

Hi Andy,

I'm trying to revive autofdo testing. One of the issues I'm running into with my setup is that PEBS doesn't work for with perf record even though PEBS is enabled.
I'm running Ubuntu 20.04 in a Hyper-V virtual machine; the processor is Icelake (GenuineIntel-6-7E).

I did the following:

1. Enabled pmu, lbr, and pebs in my Hyper-V virtual machine as described in https://docs.microsoft.com/en-us/windows-server/virtualization/hyper-v/manage/performance-monitoring-hardware
2. Verified that pmu, lbr, and pebs are enabled in the vm by running 
	erozen@erozen-Virtual-Machine:~/objdir/gcc$ dmesg | egrep -i 'pmu'
	[    0.266474] Performance Events: PEBS fmt4+, Icelake events, 32-deep LBR, full-width counters, Intel PMU driver.
3. Ran
	erozen@erozen-Virtual-Machine:~/objdir/gcc$ perf record -e cpu/event=0xc4,umask=0x20/pu -b -m8 true -v
	Error:
	The sys_perf_event_open() syscall returned with 22 (Invalid argument) for event (cpu/event=0xc4,umask=0x20/pu).
	/bin/dmesg | grep -i perf may provide additional information.

Omitting /p works fine:
	erozen@erozen-Virtual-Machine:~/objdir/gcc$ perf record -e cpu/event=0xc4,umask=0x20/u -b -m8 true -v
	[ perf record: Woken up 0 times to write data ]
	[ perf record: Captured and wrote 0.007 MB perf.data (11 samples) ]

Is there a way to get PEBS working with perf record in a vm? I would appreciate any pointers on how to investigate this.

The version of perf I'm using is 5.8.18.

Thanks,

Eugene

-----Original Message-----
From: Andi Kleen <ak@linux.intel.com> 
Sent: Friday, April 30, 2021 2:46 PM
To: Eugene Rozenfeld via Gcc <gcc@gcc.gnu.org>
Cc: Xinliang David Li <davidxl@google.com>; Richard Biener <richard.guenther@gmail.com>; Eugene Rozenfeld <Eugene.Rozenfeld@microsoft.com>; Jan Hubicka <hubicka@ucw.cz>
Subject: Re: [EXTERNAL] Re: State of AutoFDO in GCC

Eugene Rozenfeld via Gcc <gcc@gcc.gnu.org> writes:

> Is the format produced by create_gcov and expected by GCC under 
> -fauto-rpofile documented somewhere? How is it different from .gcda 
> used in FDO, e.g., as described here:
> https://nam06.safelinks.protection.outlook.com/?url=http%3A%2F%2Fsrc.gnu-darwin.org%2Fsrc%2Fcontrib%2Fgcc%2Fgcov-io.h.html&amp;data=04%7C01%7CEugene.Rozenfeld%40microsoft.com%7C6c14ea3d93c44364845008d90c214cb6%7C72f988bf86f141af91ab2d7cd011db47%7C1%7C0%7C637554159427749575%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=q9ROiOTma41UeQ%2FQG%2BUktEOrHAWonTTpcPRPmx%2Fgw0g%3D&amp;reserved=0?

I believe it's very similar.

> I would prefer that AutoFDO is not removed from GCC and it would be 
> helpful if create_gcov were restored in google/autofdo. I checked out 
> a revision before the recent merge and tried it on a simple example 
> and it seems to work.
> I'm also interested in contributing improvements for AutoFDO so will 
> try to investigate 
> https://nam06.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgcc.
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That would be great.

-Andi