On Mon, Mar 13, 2023 at 11:15:44AM -0700, Yang Shi wrote:
[...]
Just a quick summary, here we have two issues:
With command: perf record -e cs_etm/@tmc_etf63/k --kcore --per-thread \ -- taskset --cpu-list 1 uname",
perf doesn't enable "text poke" attribution.
No, it enables "text poke" and perf fails to decode coresight trace data too. It doesn't matter whether "--kcore" is after or before "-e cs/etm/@tmc_etf63/k".
Understand now. Thanks for correction, if so we can ignore this one.
Leo
On 14/03/2023 00:36, Leo Yan wrote:
On Mon, Mar 13, 2023 at 11:15:44AM -0700, Yang Shi wrote:
[...]
Just a quick summary, here we have two issues:
With command: perf record -e cs_etm/@tmc_etf63/k --kcore --per-thread \ -- taskset --cpu-list 1 uname",
perf doesn't enable "text poke" attribution.
No, it enables "text poke" and perf fails to decode coresight trace data too. It doesn't matter whether "--kcore" is after or before "-e cs/etm/@tmc_etf63/k".
Understand now. Thanks for correction, if so we can ignore this one.
Leo
To me it looks like it's only --per-thread and --kcore together that cause the issue. I can't see if that was mentioned previously in this thread.
If it is --per-thread that's causing the issue then I think I have an idea why it might be. There are some assumptions and different paths taken in decoding in that mode that aren't correct. It causes some other issues to do with ordering and timestamps as well and I wanted to fix it previously. I wouldn't say that the text-poke change has caused a regression, as decoding in this mode was always a bit buggy.
Maybe this is another reason to fix it properly.
On 14/03/2023 00:36, Leo Yan wrote:
On Mon, Mar 13, 2023 at 11:15:44AM -0700, Yang Shi wrote:
[...]
Just a quick summary, here we have two issues:
With command: perf record -e cs_etm/@tmc_etf63/k --kcore --per-thread \ -- taskset --cpu-list 1 uname",
perf doesn't enable "text poke" attribution.
No, it enables "text poke" and perf fails to decode coresight trace data too. It doesn't matter whether "--kcore" is after or before "-e cs/etm/@tmc_etf63/k".
Understand now. Thanks for correction, if so we can ignore this one.
Leo
To me it looks like it's only --per-thread and --kcore together that cause the issue. I can't see if that was mentioned previously in this thread.
If it is --per-thread that's causing the issue then I think I have an idea why it might be. There are some assumptions and different paths taken in decoding in that mode that aren't correct. It causes some other issues to do with ordering and timestamps as well and I wanted to fix it previously. I wouldn't say that the text-poke change has caused a regression, as decoding in this mode was always a bit buggy.
Maybe this is another reason to fix it properly.
On 29/03/2023 17:11, James Clark wrote:
On 14/03/2023 00:36, Leo Yan wrote:
On Mon, Mar 13, 2023 at 11:15:44AM -0700, Yang Shi wrote:
[...]
Just a quick summary, here we have two issues:
With command: perf record -e cs_etm/@tmc_etf63/k --kcore --per-thread \ -- taskset --cpu-list 1 uname",
perf doesn't enable "text poke" attribution.
No, it enables "text poke" and perf fails to decode coresight trace data too. It doesn't matter whether "--kcore" is after or before "-e cs/etm/@tmc_etf63/k".
Understand now. Thanks for correction, if so we can ignore this one.
Leo
To me it looks like it's only --per-thread and --kcore together that cause the issue. I can't see if that was mentioned previously in this thread.
If it is --per-thread that's causing the issue then I think I have an idea why it might be. There are some assumptions and different paths taken in decoding in that mode that aren't correct. It causes some other issues to do with ordering and timestamps as well and I wanted to fix it previously. I wouldn't say that the text-poke change has caused a regression, as decoding in this mode was always a bit buggy.
Maybe this is another reason to fix it properly.
Hi Yang,
I found a temporary workaround to the issue. Whenever you use --per-thread mode, force timeless mode when decoding with --itrace=Z and it works the same as it did before. For example:
perf report --itrace=Zi1000i
The reason is that the new text poke event was added with timestamps enabled. The Coresight decoder slightly incorrectly assumed that no timestamps == per-thread mode so when it sees the new event it goes into the wrong decode mode.
The assumption was never really correct so I will make a proper fix. But in the mean time the workaround should be fine.
-
James Clark -
Leo Yan