Re: perf tools: remove option --tail-synthesize ?

[Jiri Olsa]

On Wed, Nov 21, 2018 at 07:45:28AM +0000, Song Liu wrote:
> Hi,
> 
> I found perf-record --tail-synthesize without --overwrite breaks symbols
> for perf-script, perf-report, etc. For example:
> 
> [root@]# ~/perf record -ag --tail-synthesize -- sleep 1
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 1.129 MB perf.data (3531 samples) ]
> [root@]# ~/perf script | head
> swapper     0 [000] 1250675.051971:          1 cycles:ppp:
>         ffffffff81009e15 [unknown] ([unknown])
>         ffffffff81196b19 [unknown] ([unknown])
>         ffffffff81196579 [unknown] ([unknown])
>         ffffffff81110ca7 [unknown] ([unknown])
>         ffffffff81a01f4a [unknown] ([unknown])
>         ffffffff81a017bf [unknown] ([unknown])
>         ffffffff8180e17a [unknown] ([unknown])
> 
> perf-record with --overwrite does NOT have this issue.

actualy I think that now it works properly, if you turn on
task and mmap events, you'll see the samples get resolved
right after aux events are processed:

	[root@krava perf]# ./perf script --show-info --show-task-events --show-mmap-events
	...
	swapper     0 [007] 620566.187355:      64821 cycles:ppp:
		ffffffffab0b4d7c [unknown] ([unknown])
		ffffffffaba01b1f [unknown] ([unknown])
		ffffffffab75d567 [unknown] ([unknown])
		ffffffffab0e1f56 [unknown] ([unknown])
		ffffffffab0e216f [unknown] ([unknown])
		ffffffffab050dc7 [unknown] ([unknown])
		ffffffffab0000d5 [unknown] ([unknown])

	swapper     0 [000]     0.000000: PERF_RECORD_MMAP -1/0: [0xffffffffab000000(0x152c8000) @ 0xffffffffab000000]: x [kernel.kallsyms]_text
	swapper     0 [000]     0.000000: PERF_RECORD_MMAP -1/0: [0xffffffffc02c8000(0x4000) @ 0]: x /lib/modules/4.18.17-200.fc28.x86_64/kernel/drivers/thermal/int340x_thermal/int3403_thermal.ko.xz
	swapper     0 [000]     0.000000: PERF_RECORD_MMAP -1/0: [0xffffffffc02cd000(0x4000) @ 0]: x /lib/modules/4.18.17-200.fc28.x86_64/kernel/drivers/thermal/intel_pch_thermal.ko.xz
	...
	ext4-rsv-conver     0 [000]     0.000000: PERF_RECORD_COMM: ext4-rsv-conver:989/989
	perf 20063 [005] 620566.187438:    1056712 cycles:ppp:
		ffffffffab1f605d filemap_map_pages+0x9d (/usr/lib/debug/lib/modules/4.18.17-200.fc28.x86_64/vmlinux)
		ffffffffab23aaa8 __handle_mm_fault+0x1018 (/usr/lib/debug/lib/modules/4.18.17-200.fc28.x86_64/vmlinux)
		ffffffffab23ae7a handle_mm_fault+0xda (/usr/lib/debug/lib/modules/4.18.17-200.fc28.x86_64/vmlinux)
		ffffffffab06ac90 __do_page_fault+0x240 (/usr/lib/debug/lib/modules/4.18.17-200.fc28.x86_64/vmlinux)
		ffffffffab06af62 do_page_fault+0x32 (/usr/lib/debug/lib/modules/4.18.17-200.fc28.x86_64/vmlinux)
		ffffffffaba010ee page_fault+0x1e (/usr/lib/debug/lib/modules/4.18.17-200.fc28.x86_64/vmlinux)
	...

if you record with --overwrite and --tail-synthesize the aux events
will go to the top of the perf.data, so all's good

> 
> After digging into this, I found this issue is introduced by commit
> a73e24d240bc136619d382b1268f34d75c9d25ce.

right, we got rid of that, because it will store the 'current/live'
server mmaps for report/script, which is not what you want

> Reverting this commit does fix this issue. However, on a second thought,
> I feel it is probably better just drop --tail-synthesize, as it doesn't
> make much sense without --overwrite. All we need is to do tail_synthesize
> when --overwrite is set.
> 
> Thoughts?

maybe we should make --tail-synthesize non optionable for --overwrite,
and get rid of that option completely.. Wang, any idea?

but definitelly not allow that for non overwrite

thanks,
jirka